diff --git a/lib/app-wrapper.js b/lib/app-wrapper.js
index d584fbea1..6c773e1e2 100644
--- a/lib/app-wrapper.js
+++ b/lib/app-wrapper.js
@@ -109,9 +109,7 @@ function subscribe(port) {
 function unsubscribe(port) {
   // eslint-disable-next-line promise/prefer-await-to-callbacks -- Callbacks are still needed here.
   return (callback) => {
-    listeners[port] = listeners[port].filter(
-      (/** @type {Listened<unknown>} */ fn) => fn === callback
-    );
+    listeners[port] = listeners[port].filter((fn) => fn === callback);
   };
 }
 
diff --git a/lib/build.js b/lib/build.js
index 80141af98..cda241d9d 100644
--- a/lib/build.js
+++ b/lib/build.js
@@ -1,10 +1,10 @@
 /**
  * @import {AppHash, BuildResult} from './types/build';
- * @import {ApplicationElmJson} from './types/content';
+ * @import {ApplicationElmJson, ElmJson} from './types/content';
  * @import {VersionString} from './types/version';
  * @import {Options, Template} from './types/options';
  * @import {Path} from './types/path';
- * @import {CompileOptions} from '../vendor/types/node-elm-compiler';
+ * @import {CompileOptions, Sources} from '../vendor/types/node-elm-compiler';
  */
 const path = require('node:path');
 const crypto = require('node:crypto');
@@ -204,10 +204,7 @@ I can help set you up with an initial configuration if you run ${chalk.magenta('
  */
 async function buildFromGitHubTemplate(options, template) {
   Spinner.setText('Fetching template information');
-  const commit = await RemoteTemplate.getRelevantCommit(
-    options,
-    options.template
-  );
+  const commit = await RemoteTemplate.getRelevantCommit(options, template);
   const reviewElmJson = await RemoteTemplate.getRemoteElmJson(
     options,
     template,
@@ -333,6 +330,11 @@ async function createTemplateProject(
   Benchmark.end(options, 'Create template project');
 }
 
+/**
+ * @param {Options} options
+ * @param {string} userSrc
+ * @param {ApplicationElmJson} elmJson
+ */
 function updateSourceDirectories(options, userSrc, elmJson) {
   let sourceDirectories = [
     ...elmJson['source-directories'].map((directory) =>
@@ -355,13 +357,22 @@ function updateSourceDirectories(options, userSrc, elmJson) {
   };
 }
 
+/**
+ * @param {Options} options
+ * @param {string} dest
+ * @param {string} elmModulePath
+ * @param {Sources} compileTargets
+ * @param {string} elmBinary
+ * @param {boolean} isReviewApp
+ * @returns {Promise<string | null>}
+ */
 async function compileElmProject(
   options,
   dest,
   elmModulePath,
   compileTargets,
   elmBinary,
-  isReviewAppApp
+  isReviewApp
 ) {
   /** @type {CompileOptions} */
   const compileOptions = {
@@ -379,6 +390,7 @@ async function compileElmProject(
     }
   };
 
+  /** @type {string | null} */
   const resolvedElmModulePath = await new Promise((resolve) => {
     const compileProcess = elmCompiler.compile(compileTargets, compileOptions);
 
@@ -437,13 +449,13 @@ async function compileElmProject(
       }
     });
   });
-  return await OptimizeJs.optimize(
-    options,
-    resolvedElmModulePath,
-    isReviewAppApp
-  );
+  return await OptimizeJs.optimize(options, resolvedElmModulePath, isReviewApp);
 }
 
+/**
+ * @param {Options} options
+ * @param {string} stderr
+ */
 function compilationError(options, stderr) {
   if (stderr.includes('DEBUG REMNANTS')) {
     return {
@@ -457,7 +469,7 @@ function compilationError(options, stderr) {
     return {
       title: 'MODULE NOT FOUND',
       // prettier-ignore
-      message: `A module is missing in your configuration. Maybe you forgot to add some dependencies that contain the rules you wished to enable? If so, run ${chalk.magenta('elm install')} with the package name from inside ${chalk.yellow(options.userSrc(null))}.`
+      message: `A module is missing in your configuration. Maybe you forgot to add some dependencies that contain the rules you wished to enable? If so, run ${chalk.magenta('elm install')} with the package name from inside ${chalk.yellow(options.userSrc())}.`
     };
   }
 
@@ -480,6 +492,11 @@ function compilationError(options, stderr) {
   };
 }
 
+/**
+ * @param {Options} options
+ * @param {Path} reviewElmJsonPath
+ * @param {ElmJson} reviewElmJson
+ */
 function validateElmReviewVersion(options, reviewElmJsonPath, reviewElmJson) {
   if (options.localElmReviewSrc) {
     return;
@@ -533,6 +550,11 @@ of ${chalk.yellow(path.dirname(reviewElmJsonPath))}.`
   MinVersion.validate(options, reviewElmJsonPath, elmReviewVersion);
 }
 
+/**
+ * @param {Options} options
+ * @param {ApplicationElmJson} reviewElmJson
+ * @returns {Promise<void>}
+ */
 async function buildElmParser(options, reviewElmJson) {
   const elmSyntaxVersion =
     reviewElmJson.dependencies.direct['stil4m/elm-syntax'] ||
@@ -566,7 +588,7 @@ async function buildElmParser(options, reviewElmJson) {
     })
   ]);
 
-  return await compileElmProject(
+  await compileElmProject(
     options,
     buildFolder,
     elmParserPath,
diff --git a/lib/cache.js b/lib/cache.js
index f88b66ac1..dcae076cc 100644
--- a/lib/cache.js
+++ b/lib/cache.js
@@ -6,7 +6,7 @@ const FS = require('./fs-wrapper');
 const AppState = require('./state');
 
 /**
- * @template {object} T
+ * @template T
  * @param {Path} folder
  * @param {string} key
  * @param {() => Promise<T | null>} fn
@@ -39,7 +39,7 @@ const ensuredFolders = new Set();
  * Cache a file on the filesystem.
  *
  * @param {string} filepath - Path to the file ending in ".json"
- * @param {object} content
+ * @param {unknown} content
  * @returns {Promise<void>}
  */
 async function cacheJsonFile(filepath, content) {
diff --git a/lib/elm-app-worker.js b/lib/elm-app-worker.js
index c56716fbb..e8e50831a 100644
--- a/lib/elm-app-worker.js
+++ b/lib/elm-app-worker.js
@@ -1,5 +1,7 @@
 /**
  * @import {MessagePort} from 'worker_threads';
+ * @import {Ports} from './types/app';
+ * @import {SendPort} from './types/promisify-port';
  */
 const {parentPort, workerData} = require('node:worker_threads');
 const ElmCommunication = require('./elm-communication');
@@ -31,13 +33,17 @@ if (parentPort) {
  * @returns {void}
  */
 function subscribe(parentPort) {
-  parentPort.on('message', async ([port, data]) => {
-    if (port === 'startReview' || port === 'startGeneratingSuppressions') {
-      await loadCachePromise;
-    }
+  parentPort.on(
+    'message',
 
-    app.ports[port].send(data);
-  });
+    async (/** @type {[keyof Ports, unknown]}  */ [port, data]) => {
+      if (port === 'startReview' || port === 'startGeneratingSuppressions') {
+        await loadCachePromise;
+      }
+
+      /** @type {SendPort<unknown>} */ (app.ports[port]).send(data);
+    }
+  );
 
   app.ports.requestReadingFiles.subscribe((data) => {
     parentPort.postMessage(['requestReadingFiles', data]);
diff --git a/lib/elm-files.js b/lib/elm-files.js
index 39fca8a5d..c1948cbf3 100644
--- a/lib/elm-files.js
+++ b/lib/elm-files.js
@@ -1,5 +1,5 @@
 /**
- * @import {ElmFile, Source, Readme, ElmJson, ElmJsonData, SourceDirectories} from './types/content';
+ * @import {ElmFile, Source, Readme, ElmJson, ElmJsonData, SourceDirectories, Ast} from './types/content';
  * @import {ReviewOptions} from './types/options';
  * @import {Path} from './types/path';
  */
@@ -189,7 +189,7 @@ async function readFile(
     path: OsHelpers.makePathOsAgnostic(relativeFilePath),
     source,
     lastUpdatedTime,
-    ast: cachedAst || (await readAst(options, elmParserPath, source))
+    ast: cachedAst ?? (await readAst(options, elmParserPath, source))
   };
 }
 
@@ -199,7 +199,7 @@ async function readFile(
  * @param {ReviewOptions} options
  * @param {Path} elmParserPath
  * @param {Source} source
- * @returns {Promise<ElmFile | null>}
+ * @returns {Promise<Ast | null>}
  */
 async function readAst(options, elmParserPath, source) {
   const hash = Hash.hash(source);
diff --git a/lib/fs-wrapper.js b/lib/fs-wrapper.js
index 5b0fc066c..3472e0622 100644
--- a/lib/fs-wrapper.js
+++ b/lib/fs-wrapper.js
@@ -1,6 +1,6 @@
 /**
- * @import {Path} from './types/path';
  * @import {Replacer, Reviver} from './types/json';
+ * @import {Path} from './types/path';
  */
 const fs = require('graceful-fs');
 const fsp = fs.promises;
@@ -51,7 +51,7 @@ async function readFile(file, options) {
  * Write a JSON file.
  *
  * @param {string} file
- * @param {object} content
+ * @param {unknown} content
  * @param {string | number | undefined} [space=undefined]
  * @param {Replacer | undefined} [replacer=undefined]
  * @returns {Promise<void>}
diff --git a/lib/init.js b/lib/init.js
index 11dd18a26..dae014243 100644
--- a/lib/init.js
+++ b/lib/init.js
@@ -1,3 +1,8 @@
+/**
+ * @import {Options, Template} from './types/options';
+ * @import {Path} from './types/path';
+ */
+
 const path = require('node:path');
 const fs = require('graceful-fs');
 // TODO(@lishaduck) [engine:node@>=16.7.0]: Use native `cp`.
@@ -10,6 +15,10 @@ const RemoteTemplate = require('./remote-template');
 const {getElmBinary, getElmVersion} = require('./elm-binary');
 const TemplateDependencies = require('./template-dependencies');
 
+/**
+ * @param {Options} options
+ * @returns {Promise<void>}
+ */
 async function promptAndCreate(options) {
   const directory = options.initPath();
 
@@ -38,6 +47,11 @@ async function promptAndCreate(options) {
   logInit(options, directory);
 }
 
+/**
+ * @param {Options} options
+ * @param {Template} template
+ * @param {string} directory
+ */
 async function createFromTemplate(options, template, directory) {
   const configDirectory = path.join(directory, 'src');
 
@@ -73,6 +87,10 @@ async function createFromTemplate(options, template, directory) {
   );
 }
 
+/**
+ * @param {Options} options
+ * @param {Path} directory
+ */
 function logInit(options, directory) {
   const message = options.template
     ? templateInitMessage(options, directory)
@@ -96,6 +114,10 @@ ${options.template ? templateRecommendation : ''}`
   );
 }
 
+/**
+ * @param {Options} options
+ * @param {Path} directory
+ */
 function regularInitMessage(options, directory) {
   return `You can now define your review configuration by editing ${chalk.green(
     Anonymize.path(options, path.join(directory, 'src/ReviewConfig.elm'))
@@ -104,6 +126,10 @@ function regularInitMessage(options, directory) {
 
 const orange = chalk.keyword('orange');
 
+/**
+ * @param {Options} options
+ * @param {Path} directory
+ */
 function templateInitMessage(options, directory) {
   return `You chose to use someone's review configuration which can be great to get started
 but don't forget to review the configuration to make sure it fits your needs,
@@ -124,6 +150,11 @@ I recommend you use a mix of the following approaches:
 )}).
 `;
 
+/**
+ * @param {Options} options
+ * @param {Path} directory
+ * @param {string} template
+ */
 async function create(options, directory, template) {
   const configDirectory = path.join(directory, 'src');
 
@@ -135,6 +166,10 @@ async function create(options, directory, template) {
   createReviewConfig(configDirectory, template);
 }
 
+/**
+ * @param {Options} options
+ * @param {Path} directory
+ */
 async function createElmJson(options, directory) {
   const elmBinary = await getElmBinary(options);
   const elmVersion = getElmVersion(elmBinary);
@@ -149,6 +184,10 @@ async function createElmJson(options, directory) {
   );
 }
 
+/**
+ * @param {Path} directory
+ * @param {string} template
+ */
 function createReviewConfig(directory, template) {
   fsExtra.copyFileSync(
     path.join(__dirname, '../init-templates/', template),
diff --git a/lib/min-version.js b/lib/min-version.js
index 44bad626b..c134f3137 100644
--- a/lib/min-version.js
+++ b/lib/min-version.js
@@ -8,9 +8,14 @@ const chalk = require('chalk');
 const ErrorMessage = require('./error-message');
 const PathHelpers = require('./path-helpers');
 
-const minimalVersion = {major: 2, minor: 14};
-// prettier-ignore
-const supportedRange = `${minimalVersion.major}.${minimalVersion.minor}.0 <= v < ${minimalVersion.major + 1}.0.0`
+const minimalVersion = /** @type {const} */ ({major: 2, minor: 14});
+
+// TS can't do arithmetic, so make sure the cast is right when bumping the major.
+const nextMajor = /** @type {3} */ (minimalVersion.major + 1);
+
+const supportedRange = /** @type {const} */ (
+  `${minimalVersion.major}.${minimalVersion.minor}.0 <= v < ${nextMajor}.0.0`
+);
 
 /**
  * If given an input version string smaller than the hardcoded `minimalVersion`,
diff --git a/lib/new-package.js b/lib/new-package.js
index 49d34b2e5..809e15346 100644
--- a/lib/new-package.js
+++ b/lib/new-package.js
@@ -1,5 +1,7 @@
 /**
- * @import {ElmJson} from './types/content';
+ * @import {ApplicationElmJson, PackageName} from './types/content';
+ * @import {Path} from './types/path';
+ * @import {Options, RuleType} from './types/options';
  */
 const childProcess = require('node:child_process');
 const path = require('node:path');
@@ -14,6 +16,9 @@ const MinVersion = require('./min-version');
 const NewRule = require('./new-rule');
 const Spinner = require('./spinner');
 
+/**
+ * @param {Options} options
+ */
 async function create(options) {
   const onCancelOptions = {
     onCancel: () => {
@@ -25,7 +30,7 @@ async function create(options) {
   let canceled = false;
 
   const authorName =
-    options.prefilledAnswers.authorName ||
+    options.prefilledAnswers.authorName ??
     (await prompts(
       [
         {
@@ -49,7 +54,7 @@ async function create(options) {
   }
 
   const license =
-    options.prefilledAnswers.license ||
+    options.prefilledAnswers.license ??
     (await prompts(
       [
         {
@@ -73,7 +78,7 @@ async function create(options) {
     return;
   }
 
-  const ruleType = options.ruleType || (await NewRule.askForRuleType());
+  const ruleType = options.ruleType ?? (await NewRule.askForRuleType());
   if (!ruleType) {
     return;
   }
@@ -98,6 +103,9 @@ I hope you'll enjoy working with ${chalk.greenBright('elm-review')}! ❤️
   );
 }
 
+/**
+ * @param {string} packageName
+ */
 function validatePackageName(packageName) {
   if (!packageName.startsWith('elm-review-')) {
     throw new ErrorMessage.CustomError(
@@ -146,10 +154,24 @@ const elmToolingJson = {
   }
 };
 
+/**
+ * @param {Path} dir
+ * @param {string} fileName
+ * @param {string} content
+ * @returns {Promise<void>}
+ */
 async function writeFile(dir, fileName, content) {
   await FS.writeFile(path.join(dir, fileName), content);
 }
 
+/**
+ * @param {Options} options
+ * @param {string} authorName
+ * @param {PackageName} packageName
+ * @param {string} ruleName
+ * @param {RuleType} ruleType
+ * @param {string} license
+ */
 async function createProject(
   options,
   authorName,
@@ -196,7 +218,7 @@ async function createProject(
 
   // Adding package to the example's elm.json
   const previewElmJsonPath = path.join(pathToPreview, 'elm.json');
-  const previewElmJson = /** @type {ElmJson} */ (
+  const previewElmJson = /** @type {ApplicationElmJson} */ (
     await FS.readJsonFile(previewElmJsonPath)
   );
   previewElmJson['source-directories'] = [
@@ -320,6 +342,12 @@ ElmjutsuDumMyM0DuL3.elm
   Spinner.succeed();
 }
 
+/**
+ * @param {string} authorName
+ * @param {PackageName} packageName
+ * @param {string} ruleName
+ * @param {string} license
+ */
 function elmJson(authorName, packageName, ruleName, license) {
   return {
     type: 'package',
@@ -340,6 +368,11 @@ function elmJson(authorName, packageName, ruleName, license) {
   };
 }
 
+/**
+ * @param {string} authorName
+ * @param {PackageName} packageName
+ * @param {string} ruleName
+ */
 function readme(authorName, packageName, ruleName) {
   return `# ${packageName}
 
@@ -373,6 +406,10 @@ elm-review --template ${authorName}/${packageName}/example
 `;
 }
 
+/**
+ * @param {Options} options
+ * @param {PackageName} packageName
+ */
 function packageJson(options, packageName) {
   return {
     name: packageName,
diff --git a/lib/new-rule.js b/lib/new-rule.js
index 1c2d5800c..31c76c8c8 100644
--- a/lib/new-rule.js
+++ b/lib/new-rule.js
@@ -194,10 +194,18 @@ async function addRule(options, elmJson, ruleName, ruleType) {
 
   if (elmJson.type === 'package' && packageNameRegex.test(elmJson.name)) {
     console.log('Exposing the rule in elm.json');
-    if (!elmJson['exposed-modules'].includes(ruleName)) {
+
+    const exposedModules = Array.isArray(elmJson['exposed-modules'])
+      ? elmJson['exposed-modules']
+      : Object.values(elmJson['exposed-modules']).reduce((acc, items) => [
+          ...acc,
+          ...items
+        ]);
+
+    if (!exposedModules.includes(ruleName)) {
       const newElmJson = {
         ...elmJson,
-        'exposed-modules': [...elmJson['exposed-modules'], ruleName].sort()
+        'exposed-modules': [...exposedModules, ruleName].sort()
       };
 
       writeFile(dir, 'elm.json', JSON.stringify(newElmJson, null, 4));
diff --git a/lib/optimize-js.js b/lib/optimize-js.js
index 551b2194f..dfa72a890 100644
--- a/lib/optimize-js.js
+++ b/lib/optimize-js.js
@@ -1,17 +1,28 @@
+/**
+ * @import {Options} from './types/options';
+ * @import {Optimization} from './types/optimize-js';
+ */
+
 const Benchmark = require('./benchmark');
 const FS = require('./fs-wrapper');
 
-async function optimize(options, elmModulePath, isReviewAppApp) {
+/**
+ * @param {Options} options
+ * @param {string | null} elmModulePath
+ * @param {boolean} isReviewApp
+ * @returns {Promise<string | null>}
+ */
+async function optimize(options, elmModulePath, isReviewApp) {
   if (options.debug || !elmModulePath) {
     return elmModulePath;
   }
 
-  const timerId = isReviewAppApp
+  const timerId = isReviewApp
     ? 'optimizing review application'
     : 'optimizing parser application';
   Benchmark.start(options, timerId);
   const originalSource = await FS.readFile(elmModulePath);
-  const replacements = isReviewAppApp
+  const replacements = isReviewApp
     ? [
         ...performanceReplacements,
         ...cacheReplacements(options.localElmReviewSrc)
@@ -411,6 +422,10 @@ const performanceReplacements = [
   }
 ];
 
+/**
+ * @param {string | undefined} localElmReviewSrc
+ * @returns {Optimization[]}
+ */
 function cacheReplacements(localElmReviewSrc) {
   const packageName = localElmReviewSrc
     ? '$author$project'
diff --git a/lib/parse-elm.js b/lib/parse-elm.js
index 450cf5c8c..1cc71ccb9 100644
--- a/lib/parse-elm.js
+++ b/lib/parse-elm.js
@@ -4,7 +4,7 @@
  */
 
 /**
- * @import {Source, ElmFile} from './types/content';
+ * @import {Source, ElmFile, Ast} from './types/content';
  * @import {ParseJob} from './types/parse-elm';
  * @import {Path} from './types/path';
  */
@@ -58,15 +58,17 @@ function terminateWorkers() {
 /**
  * @param {Path} elmParserPath
  * @param {Source} source
- * @returns {Promise<ElmFile>}
+ * @returns {Promise<Ast>}
  */
 async function parse(elmParserPath, source) {
   return await new Promise((resolve, reject) => {
     const availableWorker = findInactiveWorker();
+
     /** @type {ParseJob} */
     const queueItem = {
       source,
       elmParserPath,
+
       callback: (/** @type {Error | undefined} */ error, result) => {
         if (error === undefined) {
           resolve(result);
diff --git a/lib/project-dependencies.js b/lib/project-dependencies.js
index 689645718..f1b0917fe 100644
--- a/lib/project-dependencies.js
+++ b/lib/project-dependencies.js
@@ -1,5 +1,16 @@
+/**
+ * @import {ElmJson} from './types/content';
+ * @import {Options} from './types/options';
+ * @import {VersionString} from './types/version';
+ */
+
 const ProjectJsonFiles = require('./project-json-files');
 
+/**
+ * @param {Options} options
+ * @param {ElmJson} elmJson
+ * @param {VersionString} elmVersion
+ */
 async function collect(options, elmJson, elmVersion) {
   const dependenciesEntries =
     elmJson.type === 'application'
@@ -19,7 +30,9 @@ async function collect(options, elmJson, elmVersion) {
 
   const projectDepsPromises = Object.entries(dependenciesEntries).map(
     async ([name, constraint]) => {
-      const packageVersion = constraint.split(' ')[0];
+      const packageVersion = /** @type {VersionString} */ (
+        constraint.split(' ')[0]
+      );
 
       const [docsJson, dependencyElmJson] = await Promise.all([
         ProjectJsonFiles.getDocsJson(
@@ -66,6 +79,10 @@ I will try to review the project anyway, but you might get unexpected results…
   return projectDeps;
 }
 
+/**
+ * @param {string} name
+ * @param {VersionString} packageVersion
+ */
 function defaultElmJson(name, packageVersion) {
   return {
     type: 'package',
diff --git a/lib/project-json-files.js b/lib/project-json-files.js
index 527ffce56..a53036a3e 100644
--- a/lib/project-json-files.js
+++ b/lib/project-json-files.js
@@ -118,7 +118,7 @@ function getPackagePathInElmHome(elmVersion, name) {
  * @param {Options} options
  * @param {VersionString} elmVersion
  * @param {string} name
- * @param {string} packageVersion
+ * @param {VersionString} packageVersion
  * @returns {Promise<unknown>}
  */
 async function getDocsJson(options, elmVersion, name, packageVersion) {
diff --git a/lib/remote-template.js b/lib/remote-template.js
index 55c47a091..424ae9124 100644
--- a/lib/remote-template.js
+++ b/lib/remote-template.js
@@ -18,6 +18,8 @@ const TemplateDependencies = require('./template-dependencies');
 // GET LATEST INFORMATION ABOUT REPOSITORY
 
 /**
+ * @param {Options} options
+ * @param {Template} template
  * @returns {Promise<string>}
  */
 async function getRelevantCommit(options, template) {
@@ -36,33 +38,42 @@ async function getRelevantCommit(options, template) {
 
 /**
  * @returns {Promise<string>}
+ * @param {Options} options
+ * @param {Template} template
  */
 async function findDefaultBranch(options, template) {
   Debug.log('Fetching default branch');
-  const body = await makeGitHubApiRequest(
-    options,
-    `https://api.github.com/repos/${template.repoName}`,
-    () => repoNotFoundErrorMessage(template.repoName)
+  const body = /** @type {{default_branch: string}} */ (
+    await makeGitHubApiRequest(
+      options,
+      `https://api.github.com/repos/${template.repoName}`,
+      () => repoNotFoundErrorMessage(template.repoName)
+    )
   );
   return body.default_branch;
 }
 
 /**
  * @returns {Promise<string>}
+ * @param {Options} options
+ * @param {Template} template
+ * @param {string} reference
  */
 async function getLatestCommitForReference(options, template, reference) {
   Debug.log(`Fetching commit ${reference}`);
-  const body = await makeGitHubApiRequest(
-    options,
-    `https://api.github.com/repos/${template.repoName}/commits/${reference}`,
-    (responseBody) => {
-      if (responseBody.message === 'Not Found') {
-        // This error means that the repo itself was not found
-        return repoNotFoundErrorMessage(template.repoName);
-      }
+  const body = /** @type {{sha: string}} */ (
+    await makeGitHubApiRequest(
+      options,
+      `https://api.github.com/repos/${template.repoName}/commits/${reference}`,
+      (responseBody) => {
+        if (responseBody.message === 'Not Found') {
+          // This error means that the repo itself was not found
+          return repoNotFoundErrorMessage(template.repoName);
+        }
 
-      return commitNotFoundErrorMessage(template.repoName, reference);
-    }
+        return commitNotFoundErrorMessage(template.repoName, reference);
+      }
+    )
   );
   return body.sha;
 }
@@ -108,6 +119,10 @@ async function getRemoteElmJson(
   return TemplateDependencies.update(options, elmJson);
 }
 
+/**
+ * @param {Template} template
+ * @param {string} commit
+ */
 async function downloadTemplateElmJson(template, commit) {
   const {repoName, pathToFolder} = template;
   const pathToFolderAsUrl = pathToFolder ? `/${pathToFolder}` : '';
@@ -165,6 +180,9 @@ elm-review in your project:
     elm-review init --template <some-configuration>`
 };
 
+/**
+ * @param {string} repoName
+ */
 function repoNotFoundErrorMessage(repoName) {
   return {
     title: 'REPOSITORY NOT FOUND',
@@ -176,6 +194,10 @@ with private ones at the moment.`
   };
 }
 
+/**
+ * @param {unknown} repoName
+ * @param {unknown} reference
+ */
 function commitNotFoundErrorMessage(repoName, reference) {
   return {
     title: 'BRANCH OR COMMIT NOT FOUND',
@@ -189,6 +211,13 @@ Check the spelling and make sure it has been pushed.`
 
 // DOWNLOAD TEMPLATE FILES
 
+/**
+ * @param {Options} options
+ * @param {Template} template
+ * @param {string} commit
+ * @param {string} basePath
+ * @param {ApplicationElmJson} reviewElmJson
+ */
 async function downloadSourceDirectories(
   options,
   template,
@@ -209,6 +238,13 @@ async function downloadSourceDirectories(
   );
 }
 
+/**
+ * @param {Options} options
+ * @param {Template} template
+ * @param {string} commit
+ * @param {string} basePath
+ * @param {string} directory
+ */
 async function downloadDirectory(
   options,
   template,
@@ -220,12 +256,15 @@ async function downloadDirectory(
   const destinationDirectory = directory.split('..').join('parent');
 
   await FS.mkdirp(path.join(basePath, destinationDirectory));
-  const fileListing = await makeGitHubApiRequest(
-    options,
-    `https://api.github.com/repos/${repoName}/contents${pathToFolder}/${directory}?ref=${commit}`
-      .split('//')
-      .join('/')
-  );
+  const fileListing =
+    /** @type {({ type: string; name: string; download_url: string; })[]} */ (
+      await makeGitHubApiRequest(
+        options,
+        `https://api.github.com/repos/${repoName}/contents${pathToFolder}/${directory}?ref=${commit}`
+          .split('//')
+          .join('/')
+      )
+    );
 
   await Promise.all(
     fileListing.map(async (fileOrDir) => {
@@ -283,7 +322,7 @@ async function downloadFile(url, dest) {
  * @param {Options} options
  * @param {string} url
  * @param {((arg: JsonResponse) => {title: string, message: string})} [handleNotFound]
- * @returns {Promise<object>}
+ * @returns {Promise<unknown>}
  */
 async function makeGitHubApiRequest(options, url, handleNotFound) {
   /** @type {OptionsOfJSONResponseBody}} */
diff --git a/lib/result-cache-worker.js b/lib/result-cache-worker.js
index a0876b0c5..c560d7c11 100644
--- a/lib/result-cache-worker.js
+++ b/lib/result-cache-worker.js
@@ -1,3 +1,6 @@
+/**
+ * @import {MessagePort} from 'node:worker_threads';
+ */
 const path = require('node:path');
 const {parentPort} = require('node:worker_threads');
 const fs = require('graceful-fs');
@@ -7,6 +10,9 @@ if (parentPort) {
   subscribe(parentPort);
 }
 
+/**
+ * @param {MessagePort} parentPort
+ */
 function subscribe(parentPort) {
   parentPort.on('message', ({filePath, cacheEntry, cacheKey}) => {
     try {
@@ -17,7 +23,9 @@ function subscribe(parentPort) {
       filePath,
       JSON.stringify(cacheEntry, ResultCacheJson.replacer, 0),
       'utf8',
-      () => parentPort?.postMessage(cacheKey)
+      () => {
+        parentPort?.postMessage(cacheKey);
+      }
     );
   });
 }
diff --git a/lib/result-cache.js b/lib/result-cache.js
index d78980b8c..f1677e2ab 100644
--- a/lib/result-cache.js
+++ b/lib/result-cache.js
@@ -1,16 +1,23 @@
 /**
  * @import {Options} from './types/options';
  * @import {Path} from './types/path';
+ * @import {CacheData, CacheEntry, CacheKey, RuleId, RuleName} from './types/result-cache';
  */
 const path = require('node:path');
+const {Worker} = require('node:worker_threads');
 const AppState = require('./state');
 const Benchmark = require('./benchmark');
 const Debug = require('./debug');
 const ResultCacheJson = require('./result-cache-json');
 const FS = require('./fs-wrapper');
 
-let worker = null;
+/** @type {Worker} */
+let worker;
+
+/** @type {Map<string, CacheEntry>} */
 const resultCache = new Map();
+
+/** @type {Map<string, (value?: unknown) => unknown>} */
 const promisesToResolve = new Map();
 
 // TODO(@jfmengels): Create an alternate version of Options used in
@@ -20,8 +27,8 @@ const promisesToResolve = new Map();
  * Load cache results.
  *
  * @param {Options} options
- * @param {string[]} ignoredDirs
- * @param {string[]} ignoredFiles
+ * @param {Path[]} ignoredDirs
+ * @param {Path[]} ignoredFiles
  * @param {Path} cacheFolder
  * @returns {Promise<void>}
  */
@@ -39,7 +46,6 @@ async function load(options, ignoredDirs, ignoredFiles, cacheFolder) {
   }
 
   if (!worker) {
-    const {Worker} = require('node:worker_threads');
     worker = new Worker(path.resolve(__dirname, 'result-cache-worker.js'));
     worker.on('message', (cacheKey) => {
       const promise = promisesToResolve.get(cacheKey);
@@ -55,11 +61,18 @@ async function load(options, ignoredDirs, ignoredFiles, cacheFolder) {
   resultCache.clear();
   globalThis.elmJsonReplacer = ResultCacheJson.replacer;
 
-  globalThis.loadResultFromCache = (ruleName, ruleId) => {
+  globalThis.loadResultFromCache = (
+    /** @type {RuleName} */ ruleName,
+    /** @type {RuleId} */ ruleId
+  ) => {
     return resultCache.get(key(ruleName, ruleId));
   };
 
-  globalThis.saveResultToCache = async (ruleName, ruleId, cacheEntry) => {
+  globalThis.saveResultToCache = async (
+    /** @type {RuleName} */ ruleName,
+    /** @type {RuleId} */ ruleId,
+    /** @type {CacheEntry} */ cacheEntry
+  ) => {
     const cacheKey = key(ruleName, ruleId);
 
     AppState.writingToFileSystemCacheStarted(cacheKey);
@@ -80,6 +93,7 @@ async function load(options, ignoredDirs, ignoredFiles, cacheFolder) {
   };
 
   Benchmark.start(options, 'Load results cache');
+  /** @type {string[]} */
   let files = await FS.readdir(cacheFolder).catch(() => []);
   if (files.length === 0) return;
   const {rulesFilter} = options;
@@ -90,28 +104,35 @@ async function load(options, ignoredDirs, ignoredFiles, cacheFolder) {
   }
 
   await Promise.all(
-    files.map(async (name) => {
-      await FS.readJsonFile(
-        path.join(cacheFolder, name),
-        ResultCacheJson.reviver
-      )
-        .then((entry) => {
-          resultCache.set(name.slice(0, -5), entry);
-        })
-        .catch(() => {
-          Debug.log(
-            `Ignoring results cache for ${name} as it could not be read`
-          );
-        });
+    files.map(async (/** @type {string} */ name) => {
+      try {
+        const entry = await FS.readJsonFile(
+          path.join(cacheFolder, name),
+          ResultCacheJson.reviver
+        );
+        resultCache.set(name.slice(0, -5), entry);
+      } catch {
+        Debug.log(`Ignoring results cache for ${name} as it could not be read`);
+      }
     })
   );
   Benchmark.end(options, 'Load results cache');
 }
 
+/**
+ *
+ * @param {RuleName} ruleName
+ * @param {RuleId} ruleId
+ * @returns {CacheKey}
+ */
 function key(ruleName, ruleId) {
-  return ruleName + '-' + ruleId;
+  return /** @type {CacheKey} */ (ruleName + '-' + ruleId);
 }
 
+/**
+ * @param {Options} options
+ * @param {CacheData} data
+ */
 async function saveToFile(options, data) {
   if (worker) {
     return await new Promise((resolve) => {
diff --git a/lib/review-dependencies.js b/lib/review-dependencies.js
index 3e524be84..3f05a1f2e 100644
--- a/lib/review-dependencies.js
+++ b/lib/review-dependencies.js
@@ -1,5 +1,14 @@
+/**
+ * @import {ApplicationDependencyList, PackageElmJson, PackageName} from './types/content';
+ * @import {VersionString} from './types/version';
+ */
+
 const ProjectJsonFiles = require('./project-json-files');
 
+/**
+ * @param {ApplicationDependencyList} reviewDirectDependencies
+ * @param {VersionString} elmVersion
+ */
 async function collectRuleLinks(reviewDirectDependencies, elmVersion) {
   const elmJsonForReviewDependenciesPromises = Object.entries(
     reviewDirectDependencies
@@ -24,6 +33,10 @@ async function collectRuleLinks(reviewDirectDependencies, elmVersion) {
   );
 }
 
+/**
+ * @param {ApplicationDependencyList} reviewDirectDependencies
+ * @param {PackageElmJson[]} elmJsonForReviewDependencies
+ */
 function computeLinksToRuleDocs(
   reviewDirectDependencies,
   elmJsonForReviewDependencies
@@ -42,19 +55,28 @@ function computeLinksToRuleDocs(
         ? dep['exposed-modules']
         : Object.values(dep['exposed-modules']).reduce((acc, items) => [
             ...acc,
-            items
+            ...items
           ]);
 
       for (const moduleName of exposedModules) {
-        acc[moduleName] = linkToModule(depName, packageVersion, moduleName);
+        acc[moduleName] = linkToModule(
+          /** @type {PackageName} */ (depName),
+          packageVersion,
+          moduleName
+        );
       }
 
       return acc;
     },
-    {}
+    /** @type {Record<string, string>} */ ({})
   );
 }
 
+/**
+ * @param {PackageName} dependencyName
+ * @param {VersionString} packageVersion
+ * @param {string} moduleName
+ */
 function linkToModule(dependencyName, packageVersion, moduleName) {
   const urlModuleName = moduleName.split('.').join('-');
   return `https://package.elm-lang.org/packages/${dependencyName}/${packageVersion}/${urlModuleName}`;
diff --git a/lib/template-dependencies.js b/lib/template-dependencies.js
index 1042b0507..1a6cf1c59 100644
--- a/lib/template-dependencies.js
+++ b/lib/template-dependencies.js
@@ -253,7 +253,7 @@ function filterOutDuplicateDependenciesForSection(
 ) {
   return Object.fromEntries(
     Object.entries(testDependencies).filter(
-      ([pkg]) => !regularDependencies[pkg]
+      ([pkg]) => !regularDependencies[/** @type {PackageName} */ (pkg)]
     )
   );
 }
@@ -266,13 +266,17 @@ function filterOutDuplicateDependenciesForSection(
  * @returns {ApplicationElmJson}
  */
 function update(options, elmJson) {
+  /** @type {PackageDependencyList} */
   const extra = {
     'stil4m/elm-syntax': '7.0.0 <= v < 8.0.0',
     'jfmengels/elm-review': MinVersion.supportedRange
   };
 
   for (const [pkg, version] of Object.entries(elmJson.dependencies.direct)) {
-    extra[pkg] = `${version} <= v < ${nextVersion(version, 'major')}`;
+    extra[/** @type {PackageName} */ (pkg)] = `${version} <= v < ${nextVersion(
+      version,
+      'major'
+    )}`;
   }
 
   delete elmJson.dependencies.direct['jfmengels/elm-review'];
diff --git a/lib/types/app.ts b/lib/types/app.ts
index 986a53d9d..89a20f7c0 100644
--- a/lib/types/app.ts
+++ b/lib/types/app.ts
@@ -5,14 +5,15 @@ import type {
   ElmJsonData,
   LinksToRuleDocs,
   NonElmFiles,
-  Readme
-} from './content.js';
-import type {Flags} from './flags.js';
-import type {Path} from './path.js';
-import type {SendPort, SubscribePort} from './promisify-port.js';
-import type {FilesProposedByCurrentFix} from './state.js';
-import type {StyledMessage} from './styled-message.js';
-import type {SuppressedErrorsFile} from './suppressed.js';
+  Readme,
+  Source
+} from './content.ts';
+import type {Flags} from './flags.ts';
+import type {Path} from './path.ts';
+import type {SendPort, SubscribePort} from './promisify-port.ts';
+import type {FilesProposedByCurrentFix} from './state.ts';
+import type {StyledMessage} from './styled-message.ts';
+import type {SuppressedErrorsFile} from './suppressed.ts';
 
 export type Elm = {
   Elm: {
@@ -54,7 +55,7 @@ export type Ports = {
 
   acknowledgeFileReceipt: SubscribePort<FileReceipt>;
   askConfirmationToFix: SubscribePort<AutofixRequest>;
-  cacheFile: SubscribePort<{source: string; ast: Ast}>;
+  cacheFile: SubscribePort<CacheRequest>;
   fixConfirmationStatus: SubscribePort<boolean>;
   askForFixConfirmationStatus: SendPort<null>;
   abort: SubscribePort<string>;
@@ -66,9 +67,11 @@ export type Ports = {
 
 export type FileReceipt = {
   path: Path;
-  cacheRequest: {source: string; ast: Ast} | null;
+  cacheRequest: CacheRequest | null;
 };
 
+export type CacheRequest = {source: Source; ast: Ast};
+
 export type AutofixRequest = {
   confirmationMessage: StyledMessage;
   clearFixLine: boolean;
diff --git a/lib/types/build.ts b/lib/types/build.ts
index 1f8e1697b..d3b7506f8 100644
--- a/lib/types/build.ts
+++ b/lib/types/build.ts
@@ -1,5 +1,5 @@
-import type {ApplicationElmJson} from './content.js';
-import type {Path} from './path.js';
+import type {ApplicationElmJson} from './content.ts';
+import type {Path} from './path.ts';
 
 export type BuildResult = {
   elmModulePath: Path | null;
diff --git a/lib/types/content.ts b/lib/types/content.ts
index d96f2968a..11b53d666 100644
--- a/lib/types/content.ts
+++ b/lib/types/content.ts
@@ -1,5 +1,5 @@
-import type {VersionRange, VersionString} from './version.js';
-import type {Path} from './path.js';
+import type {VersionRange, VersionString} from './version.ts';
+import type {Path} from './path.ts';
 
 export type File = {
   path: Path;
@@ -9,7 +9,7 @@ export type File = {
 export type ElmFile = {
   path: Path;
   source: Source;
-  ast?: Ast;
+  ast?: Ast | null;
   lastUpdatedTime?: Date | null;
 };
 
@@ -54,7 +54,7 @@ export type PackageElmJson = {
   summary: string;
   license: string;
   version: VersionString;
-  'exposed-modules': (string | Record<string, string>)[];
+  'exposed-modules': string[] | Record<string, string[]>;
   'elm-version': VersionRange;
   dependencies: PackageDependencyList;
   'test-dependencies': PackageDependencyList;
@@ -75,4 +75,4 @@ export type LinksToRuleDocs = Record<string, string>;
 
 export type Source = string;
 
-export type Ast = unknown;
+export type Ast = Record<string, unknown>;
diff --git a/lib/types/flags.ts b/lib/types/flags.ts
index 0f83f5142..2ca0c7880 100644
--- a/lib/types/flags.ts
+++ b/lib/types/flags.ts
@@ -1,5 +1,5 @@
-import type {FixMode} from './fix.js';
-import type {OptionsBase} from './options.js';
+import type {FixMode} from './fix.ts';
+import type {OptionsBase} from './options.ts';
 
 export type Flags = OptionsBase & {
   resultCacheFolder: string;
diff --git a/lib/types/optimize-js.ts b/lib/types/optimize-js.ts
new file mode 100644
index 000000000..448a9d89c
--- /dev/null
+++ b/lib/types/optimize-js.ts
@@ -0,0 +1,4 @@
+export type Optimization = {
+  target: string;
+  replacement: string;
+};
diff --git a/lib/types/options.ts b/lib/types/options.ts
index 8ee368fec..4abdfabde 100644
--- a/lib/types/options.ts
+++ b/lib/types/options.ts
@@ -1,5 +1,5 @@
-import type {AppHash} from './build.js';
-import type {Path} from './path.js';
+import type {AppHash} from './build.ts';
+import type {Path} from './path.ts';
 
 export type OptionsBase = {
   debug: boolean;
diff --git a/lib/types/parse-elm.ts b/lib/types/parse-elm.ts
index 24269c9f3..09cfcb255 100644
--- a/lib/types/parse-elm.ts
+++ b/lib/types/parse-elm.ts
@@ -1,16 +1,15 @@
-import {ElmFile, Source} from './content.js';
-import {Path} from './path.js';
-import type {SendPort, SubscribePort} from './promisify-port.js';
+import type {Ast, ElmFile, Source} from './content.ts';
+import type {Path} from './path.ts';
+import type {SendPort, SubscribePort} from './promisify-port.ts';
 
 export type ParseJob = {
   elmParserPath: Path;
   source: Source;
-  callback: Callback;
-};
 
-type Callback = {
-  (error: Error): void;
-  (error: undefined, result: ElmFile): void;
+  callback: {
+    (error: Error): void;
+    (error: undefined, result: Ast): void;
+  };
 };
 
 export type ParserApp = {
diff --git a/lib/types/result-cache.ts b/lib/types/result-cache.ts
new file mode 100644
index 000000000..445fb28fa
--- /dev/null
+++ b/lib/types/result-cache.ts
@@ -0,0 +1,32 @@
+import type {Replacer} from './json.ts';
+import type {Path} from './path.ts';
+
+declare global {
+  // eslint-disable-next-line no-var -- See discussion at typescript-eslint/typescript-eslint#7941.
+  var loadResultFromCache:
+    | (() => null)
+    | ((ruleName: RuleName, ruleId: RuleId) => CacheEntry);
+
+  // eslint-disable-next-line no-var -- See discussion at typescript-eslint/typescript-eslint#7941.
+  var saveResultToCache:
+    | (() => void)
+    | ((
+        ruleName: RuleName,
+        ruleId: RuleId,
+        cacheEntry: CacheEntry
+      ) => Promise<void>);
+
+  // eslint-disable-next-line no-var -- See discussion at typescript-eslint/typescript-eslint#7941.
+  var elmJsonReplacer: Replacer;
+}
+
+export type RuleName = string;
+export type RuleId = string;
+export type CacheEntry = unknown;
+export type CacheKey = `${RuleName}-${RuleId}}`;
+
+export type CacheData = {
+  filePath: Path;
+  cacheEntry: CacheEntry;
+  cacheKey: CacheKey;
+};
diff --git a/lib/types/state.ts b/lib/types/state.ts
index 325e082c5..5fe394b89 100644
--- a/lib/types/state.ts
+++ b/lib/types/state.ts
@@ -1,5 +1,5 @@
-import type {ElmFile, File, Readme} from './content.js';
-import type {Path} from './path.js';
+import type {ElmFile, File, Readme} from './content.ts';
+import type {Path} from './path.ts';
 
 export type Model = {
   elmFilesCacheForWatch: Map<Path, ElmFile>;
diff --git a/lib/types/suppressed.ts b/lib/types/suppressed.ts
index 9269d1e94..027506802 100644
--- a/lib/types/suppressed.ts
+++ b/lib/types/suppressed.ts
@@ -1,4 +1,4 @@
-import type {Path} from './path.js';
+import type {Path} from './path.ts';
 
 export type SuppressedErrorsFile = {
   rule: string;
diff --git a/lib/types/watch.ts b/lib/types/watch.ts
index b9542a8cb..e432a7ab2 100644
--- a/lib/types/watch.ts
+++ b/lib/types/watch.ts
@@ -1,11 +1,11 @@
-import type {App} from './app.js';
+import type {App} from './app.ts';
 import type {
   ApplicationElmJson,
   ElmFile,
   ElmJsonData,
   ExtraFileRequest
-} from './content.js';
-import type {Path} from './path.js';
+} from './content.ts';
+import type {Path} from './path.ts';
 
 export type WatchOptions = {
   app: App;
diff --git a/new-package/elm-review-package-tests/check-previews-compile.js b/new-package/elm-review-package-tests/check-previews-compile.js
index 73621f648..7df56f84e 100644
--- a/new-package/elm-review-package-tests/check-previews-compile.js
+++ b/new-package/elm-review-package-tests/check-previews-compile.js
@@ -14,6 +14,9 @@ for (const example of findPreviewConfigurations()) {
   checkThatExampleCompiles(example);
 }
 
+/**
+ * @param {string} exampleConfiguration
+ */
 function checkThatExampleCompiles(exampleConfiguration) {
   const exampleConfigurationElmJson = require(`${exampleConfiguration}/elm.json`);
 
@@ -62,10 +65,17 @@ and make the necessary changes to make it compile.`
   }
 }
 
+/**
+ * @param {string} config
+ */
 function success(config) {
   console.log(`${Ansi.green('✔')} ${path.relative(root, config)}/ compiles`);
 }
 
+/**
+ * @param {string} exampleConfiguration
+ * @param {Record<string, string>} previewDependencies
+ */
 function checkDepsAreCompatible(exampleConfiguration, previewDependencies) {
   for (const [depName, constraint] of Object.entries(packageDependencies)) {
     if (!(depName in previewDependencies)) {
@@ -94,6 +104,12 @@ function checkDepsAreCompatible(exampleConfiguration, previewDependencies) {
   }
 }
 
+/**
+ * @param {string} exampleConfiguration
+ * @param {string} depName
+ * @param {string} constraint
+ * @param {string} version
+ */
 function checkConstraint(exampleConfiguration, depName, constraint, version) {
   const [minVersion] = constraint.split(' <= v < ').map(splitVersion);
   const previewVersion = splitVersion(version);
@@ -110,6 +126,9 @@ function checkConstraint(exampleConfiguration, depName, constraint, version) {
   }
 }
 
+/**
+ * @param {string} version
+ */
 function splitVersion(version) {
   return version.split('.').map((n) => Number.parseInt(n, 10));
 }
diff --git a/new-package/elm-review-package-tests/helpers/ansi.js b/new-package/elm-review-package-tests/helpers/ansi.js
index fee727b7d..5eaa78f5a 100644
--- a/new-package/elm-review-package-tests/helpers/ansi.js
+++ b/new-package/elm-review-package-tests/helpers/ansi.js
@@ -1,13 +1,22 @@
+/**
+ * @param {string} text
+ */
 function red(text) {
-  return '\u001B[31m' + text + '\u001B[39m';
+  return `\u001B[31m${text}\u001B[39m`;
 }
 
+/**
+ * @param {string} text
+ */
 function green(text) {
-  return '\u001B[32m' + text + '\u001B[39m';
+  return `\u001B[32m${text}\u001B[39m`;
 }
 
+/**
+ * @param {string} text
+ */
 function yellow(text) {
-  return '\u001B[33m' + text + '\u001B[39m';
+  return `\u001B[33m${text}\u001B[39m`;
 }
 
 module.exports = {
diff --git a/new-package/maintenance/update-examples-from-preview.js b/new-package/maintenance/update-examples-from-preview.js
index 9d16a5bec..bd82369e8 100755
--- a/new-package/maintenance/update-examples-from-preview.js
+++ b/new-package/maintenance/update-examples-from-preview.js
@@ -16,6 +16,18 @@ if (require.main === module) {
 
 // Find all elm.json files
 
+/**
+ * @typedef {object} ApplicationElmJson
+ * @property {string[]} source-directories
+ * @property {DependencyList} dependencies
+ */
+
+/**
+ * @typedef {object} DependencyList
+ * @property {Record<string, string>} direct
+ * @property {Record<string, string>} indirect
+ */
+
 function copyPreviewsToExamples() {
   const previewFolders = findPreviewConfigurations();
   for (const folder of previewFolders) {
@@ -23,6 +35,9 @@ function copyPreviewsToExamples() {
   }
 }
 
+/**
+ * @param {string} pathToPreviewFolder
+ */
 function copyPreviewToExample(pathToPreviewFolder) {
   const pathToExampleFolder = `${pathToPreviewFolder}/`.replace(
     /preview/g,
@@ -32,7 +47,9 @@ function copyPreviewToExample(pathToPreviewFolder) {
   fs.copySync(pathToPreviewFolder, pathToExampleFolder, {overwrite: true});
 
   const pathToElmJson = path.resolve(pathToExampleFolder, 'elm.json');
-  const elmJson = fs.readJsonSync(pathToElmJson);
+  const elmJson = /** @type {ApplicationElmJson} */ (
+    fs.readJsonSync(pathToElmJson)
+  );
 
   // Remove the source directory pointing to the package's src/
   elmJson['source-directories'] = elmJson['source-directories'].filter(
diff --git a/package.json b/package.json
index 8595bba12..9f30f108f 100644
--- a/package.json
+++ b/package.json
@@ -56,7 +56,7 @@
     "test": "turbo run testing check-engines --continue",
     "test-run": "(cd test/ && ./run.sh)",
     "test-run-record": "(cd test/ && ./run.sh record)",
-    "tsc": "tsc && tsc --project tsconfig.no-implicit-any.json",
+    "tsc": "tsc",
     "tsc-watch": "tsc --watch"
   },
   "dependencies": {
diff --git a/test/jest-helpers/types/cli.ts b/test/jest-helpers/types/cli.ts
index 52b452e90..a986985d1 100644
--- a/test/jest-helpers/types/cli.ts
+++ b/test/jest-helpers/types/cli.ts
@@ -1,4 +1,4 @@
-import type {ReportMode} from '../../../lib/types/options.js';
+import type {ReportMode} from '../../../lib/types/options.ts';
 
 export type Options = {
   project?: string;
diff --git a/test/run-snapshots/elm-review-something-for-new-rule/elm-review-package-tests/check-previews-compile.js b/test/run-snapshots/elm-review-something-for-new-rule/elm-review-package-tests/check-previews-compile.js
index 7ea9eddc2..a577b2c98 100644
--- a/test/run-snapshots/elm-review-something-for-new-rule/elm-review-package-tests/check-previews-compile.js
+++ b/test/run-snapshots/elm-review-something-for-new-rule/elm-review-package-tests/check-previews-compile.js
@@ -13,6 +13,9 @@ for (const example of findPreviewConfigurations()) {
   checkThatExampleCompiles(example);
 }
 
+/**
+ * @param {string} exampleConfiguration
+ */
 function checkThatExampleCompiles(exampleConfiguration) {
   const exampleConfigurationElmJson = require(`${exampleConfiguration}/elm.json`);
 
@@ -61,10 +64,17 @@ and make the necessary changes to make it compile.`
   }
 }
 
+/**
+ * @param {string} config
+ */
 function success(config) {
   console.log(`${Ansi.green('✔')} ${path.relative(root, config)}/ compiles`);
 }
 
+/**
+ * @param {string} exampleConfiguration
+ * @param {Record<string, string>} previewDependencies
+ */
 function checkDepsAreCompatible(exampleConfiguration, previewDependencies) {
   for (const [depName, constraint] of Object.entries(packageDependencies)) {
     if (!(depName in previewDependencies)) {
@@ -93,6 +103,12 @@ function checkDepsAreCompatible(exampleConfiguration, previewDependencies) {
   }
 }
 
+/**
+ * @param {string} exampleConfiguration
+ * @param {string} depName
+ * @param {string} constraint
+ * @param {string} version
+ */
 function checkConstraint(exampleConfiguration, depName, constraint, version) {
   const [minVersion] = constraint.split(' <= v < ').map(splitVersion);
   const previewVersion = splitVersion(version);
@@ -109,6 +125,9 @@ function checkConstraint(exampleConfiguration, depName, constraint, version) {
   }
 }
 
+/**
+ * @param {string} version
+ */
 function splitVersion(version) {
   return version.split('.').map((n) => Number.parseInt(n, 10));
 }
diff --git a/test/run-snapshots/elm-review-something-for-new-rule/elm-review-package-tests/helpers/ansi.js b/test/run-snapshots/elm-review-something-for-new-rule/elm-review-package-tests/helpers/ansi.js
index fee727b7d..5eaa78f5a 100644
--- a/test/run-snapshots/elm-review-something-for-new-rule/elm-review-package-tests/helpers/ansi.js
+++ b/test/run-snapshots/elm-review-something-for-new-rule/elm-review-package-tests/helpers/ansi.js
@@ -1,13 +1,22 @@
+/**
+ * @param {string} text
+ */
 function red(text) {
-  return '\u001B[31m' + text + '\u001B[39m';
+  return `\u001B[31m${text}\u001B[39m`;
 }
 
+/**
+ * @param {string} text
+ */
 function green(text) {
-  return '\u001B[32m' + text + '\u001B[39m';
+  return `\u001B[32m${text}\u001B[39m`;
 }
 
+/**
+ * @param {string} text
+ */
 function yellow(text) {
-  return '\u001B[33m' + text + '\u001B[39m';
+  return `\u001B[33m${text}\u001B[39m`;
 }
 
 module.exports = {
diff --git a/test/run-snapshots/elm-review-something-for-new-rule/maintenance/update-examples-from-preview.js b/test/run-snapshots/elm-review-something-for-new-rule/maintenance/update-examples-from-preview.js
index 9d16a5bec..bd82369e8 100755
--- a/test/run-snapshots/elm-review-something-for-new-rule/maintenance/update-examples-from-preview.js
+++ b/test/run-snapshots/elm-review-something-for-new-rule/maintenance/update-examples-from-preview.js
@@ -16,6 +16,18 @@ if (require.main === module) {
 
 // Find all elm.json files
 
+/**
+ * @typedef {object} ApplicationElmJson
+ * @property {string[]} source-directories
+ * @property {DependencyList} dependencies
+ */
+
+/**
+ * @typedef {object} DependencyList
+ * @property {Record<string, string>} direct
+ * @property {Record<string, string>} indirect
+ */
+
 function copyPreviewsToExamples() {
   const previewFolders = findPreviewConfigurations();
   for (const folder of previewFolders) {
@@ -23,6 +35,9 @@ function copyPreviewsToExamples() {
   }
 }
 
+/**
+ * @param {string} pathToPreviewFolder
+ */
 function copyPreviewToExample(pathToPreviewFolder) {
   const pathToExampleFolder = `${pathToPreviewFolder}/`.replace(
     /preview/g,
@@ -32,7 +47,9 @@ function copyPreviewToExample(pathToPreviewFolder) {
   fs.copySync(pathToPreviewFolder, pathToExampleFolder, {overwrite: true});
 
   const pathToElmJson = path.resolve(pathToExampleFolder, 'elm.json');
-  const elmJson = fs.readJsonSync(pathToElmJson);
+  const elmJson = /** @type {ApplicationElmJson} */ (
+    fs.readJsonSync(pathToElmJson)
+  );
 
   // Remove the source directory pointing to the package's src/
   elmJson['source-directories'] = elmJson['source-directories'].filter(
diff --git a/test/run-snapshots/elm-review-something/elm-review-package-tests/check-previews-compile.js b/test/run-snapshots/elm-review-something/elm-review-package-tests/check-previews-compile.js
index 7ea9eddc2..a577b2c98 100644
--- a/test/run-snapshots/elm-review-something/elm-review-package-tests/check-previews-compile.js
+++ b/test/run-snapshots/elm-review-something/elm-review-package-tests/check-previews-compile.js
@@ -13,6 +13,9 @@ for (const example of findPreviewConfigurations()) {
   checkThatExampleCompiles(example);
 }
 
+/**
+ * @param {string} exampleConfiguration
+ */
 function checkThatExampleCompiles(exampleConfiguration) {
   const exampleConfigurationElmJson = require(`${exampleConfiguration}/elm.json`);
 
@@ -61,10 +64,17 @@ and make the necessary changes to make it compile.`
   }
 }
 
+/**
+ * @param {string} config
+ */
 function success(config) {
   console.log(`${Ansi.green('✔')} ${path.relative(root, config)}/ compiles`);
 }
 
+/**
+ * @param {string} exampleConfiguration
+ * @param {Record<string, string>} previewDependencies
+ */
 function checkDepsAreCompatible(exampleConfiguration, previewDependencies) {
   for (const [depName, constraint] of Object.entries(packageDependencies)) {
     if (!(depName in previewDependencies)) {
@@ -93,6 +103,12 @@ function checkDepsAreCompatible(exampleConfiguration, previewDependencies) {
   }
 }
 
+/**
+ * @param {string} exampleConfiguration
+ * @param {string} depName
+ * @param {string} constraint
+ * @param {string} version
+ */
 function checkConstraint(exampleConfiguration, depName, constraint, version) {
   const [minVersion] = constraint.split(' <= v < ').map(splitVersion);
   const previewVersion = splitVersion(version);
@@ -109,6 +125,9 @@ function checkConstraint(exampleConfiguration, depName, constraint, version) {
   }
 }
 
+/**
+ * @param {string} version
+ */
 function splitVersion(version) {
   return version.split('.').map((n) => Number.parseInt(n, 10));
 }
diff --git a/test/run-snapshots/elm-review-something/elm-review-package-tests/helpers/ansi.js b/test/run-snapshots/elm-review-something/elm-review-package-tests/helpers/ansi.js
index fee727b7d..5eaa78f5a 100644
--- a/test/run-snapshots/elm-review-something/elm-review-package-tests/helpers/ansi.js
+++ b/test/run-snapshots/elm-review-something/elm-review-package-tests/helpers/ansi.js
@@ -1,13 +1,22 @@
+/**
+ * @param {string} text
+ */
 function red(text) {
-  return '\u001B[31m' + text + '\u001B[39m';
+  return `\u001B[31m${text}\u001B[39m`;
 }
 
+/**
+ * @param {string} text
+ */
 function green(text) {
-  return '\u001B[32m' + text + '\u001B[39m';
+  return `\u001B[32m${text}\u001B[39m`;
 }
 
+/**
+ * @param {string} text
+ */
 function yellow(text) {
-  return '\u001B[33m' + text + '\u001B[39m';
+  return `\u001B[33m${text}\u001B[39m`;
 }
 
 module.exports = {
diff --git a/test/run-snapshots/elm-review-something/maintenance/update-examples-from-preview.js b/test/run-snapshots/elm-review-something/maintenance/update-examples-from-preview.js
index 9d16a5bec..bd82369e8 100755
--- a/test/run-snapshots/elm-review-something/maintenance/update-examples-from-preview.js
+++ b/test/run-snapshots/elm-review-something/maintenance/update-examples-from-preview.js
@@ -16,6 +16,18 @@ if (require.main === module) {
 
 // Find all elm.json files
 
+/**
+ * @typedef {object} ApplicationElmJson
+ * @property {string[]} source-directories
+ * @property {DependencyList} dependencies
+ */
+
+/**
+ * @typedef {object} DependencyList
+ * @property {Record<string, string>} direct
+ * @property {Record<string, string>} indirect
+ */
+
 function copyPreviewsToExamples() {
   const previewFolders = findPreviewConfigurations();
   for (const folder of previewFolders) {
@@ -23,6 +35,9 @@ function copyPreviewsToExamples() {
   }
 }
 
+/**
+ * @param {string} pathToPreviewFolder
+ */
 function copyPreviewToExample(pathToPreviewFolder) {
   const pathToExampleFolder = `${pathToPreviewFolder}/`.replace(
     /preview/g,
@@ -32,7 +47,9 @@ function copyPreviewToExample(pathToPreviewFolder) {
   fs.copySync(pathToPreviewFolder, pathToExampleFolder, {overwrite: true});
 
   const pathToElmJson = path.resolve(pathToExampleFolder, 'elm.json');
-  const elmJson = fs.readJsonSync(pathToElmJson);
+  const elmJson = /** @type {ApplicationElmJson} */ (
+    fs.readJsonSync(pathToElmJson)
+  );
 
   // Remove the source directory pointing to the package's src/
   elmJson['source-directories'] = elmJson['source-directories'].filter(
diff --git a/tsconfig.json b/tsconfig.json
index 9223b5167..21c100fe3 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -13,11 +13,8 @@
     "noImplicitThis": true,
     "resolveJsonModule": true,
     "skipLibCheck": true,
-    "strictBindCallApply": true,
-    "strictFunctionTypes": true,
-    "strictPropertyInitialization": true,
-    "strictNullChecks": true,
-    "strictBuiltinIteratorReturn": true,
+    "strict": true,
+    "useUnknownInCatchVariables": false,
     "noUncheckedSideEffectImports": true,
     "noFallthroughCasesInSwitch": true,
     "noUnusedParameters": true,
diff --git a/tsconfig.no-implicit-any.json b/tsconfig.no-implicit-any.json
deleted file mode 100644
index 4ac7ad0c3..000000000
--- a/tsconfig.no-implicit-any.json
+++ /dev/null
@@ -1,56 +0,0 @@
-{
-  "extends": "./tsconfig.json",
-  "compilerOptions": {
-    "noImplicitAny": true,
-    "tsBuildInfoFile": "node_modules/.cache/tsbuildinfo.no-implicit-any.json"
-  },
-  "include": [
-    "lib/types/**/*.ts",
-    "lib/anonymize.js",
-    "lib/benchmark.js",
-    "lib/cache.js",
-    "lib/debug.js",
-    "lib/dependency-provider.js",
-    "lib/elm-communication.js",
-    "lib/elm-files.js",
-    "lib/extra-files.js",
-    "lib/error-message.js",
-    "lib/flags.js",
-    "lib/fs-wrapper.js",
-    "lib/hash.js",
-    "lib/help.js",
-    "lib/load-compiled-app.js",
-    "lib/min-version.js",
-    "lib/new-rule.js",
-    "lib/npx.js",
-    "lib/options.js",
-    "lib/os-helpers.js",
-    "lib/parse-elm.js",
-    "lib/parse-elm-worker.js",
-    "lib/path-helpers.js",
-    "lib/project-json-files.js",
-    "lib/promisify-port.js",
-    "lib/report.js",
-    "lib/result-cache-json.js",
-    "lib/spinner.js",
-    "lib/state.js",
-    "lib/styled-message.js",
-    "lib/suppressed-errors.js",
-    "lib/sync-get.js",
-    "lib/sync-get-worker.js",
-    "lib/utils.js",
-    "test/jest-helpers/cli.js",
-    "test/jest-helpers/types/cli.ts",
-    "test/flags.test.js",
-    "test/help.test.js",
-    "test/path-helpers.test.js",
-    "test/review-local-path.js",
-    "test/review.test.js",
-    "test/snapshotter.js",
-    "test/suppress.test.js",
-    "test/version.test.js",
-    "vendor/exit.js",
-    "vendor/node-elm-compiler.js",
-    "jest.config.js"
-  ]
-}
diff --git a/turbo.json b/turbo.json
index 17c3ce63f..3c87cf5f7 100644
--- a/turbo.json
+++ b/turbo.json
@@ -30,8 +30,18 @@
         "test-run"
       ]
     },
+    "testing:offline": {
+      "dependsOn": [
+        "elm-tests",
+        "elm-format",
+        "tsc",
+        "eslint-check",
+        "prettier-check",
+        "jest"
+      ]
+    },
     "eslint-check": {
-      "inputs": ["lib/", "vendor/", ".eslintrc.js"]
+      "inputs": ["lib/", "vendor/", ".eslintrc.js", "tsconfig.json"]
     },
     "eslint-fix": {
       "inputs": [
@@ -103,6 +113,7 @@
         "tsconfig.*.json"
       ],
       "outputs": ["node_modules/.cache/tsbuildinfo.json"],
+      "cache": false,
       "persistent": true
     },
     "elm-tests": {
diff --git a/vendor/node-elm-compiler.js b/vendor/node-elm-compiler.js
index cee54136a..94fab216f 100644
--- a/vendor/node-elm-compiler.js
+++ b/vendor/node-elm-compiler.js
@@ -133,6 +133,7 @@ function compilerErrorToString(err, pathToElm) {
 /**
  * @param {Sources} sources
  * @param {CompileOptions} options
+ * @returns {ChildProcess}
  */
 function compile(sources, options) {
   var optionsWithDefaults = prepareOptions(options, options.spawn || spawn);
@@ -141,7 +142,7 @@ function compile(sources, options) {
   try {
     return runCompiler(sources, optionsWithDefaults, pathToElm).on(
       'error',
-      function (/** @type {unknown} */ err) {
+      function (err) {
         throw err;
       }
     );