diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 0000000..887a2c1
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1,2 @@
+# SCM syntax highlighting & preventing 3-way merges
+pixi.lock merge=binary linguist-language=YAML linguist-generated=true
diff --git a/.github/workflows/release_schedule.yaml b/.github/workflows/release_schedule.yaml
new file mode 100644
index 0000000..0e79fe8
--- /dev/null
+++ b/.github/workflows/release_schedule.yaml
@@ -0,0 +1,52 @@
+name: Generate release schedule artifacts
+on:
+  schedule:
+    # At 00:00 on day-of-month 1 in every 3rd month. (i.e. every quarter)
+    - cron: "0 0 1 */3 *"
+  # On demand
+  workflow_dispatch:
+
+jobs:
+  create-artifacts:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          # We're going to make a tag that we can we release so we'll need the full history for that
+          fetch-depth: 0
+      - name: Set up Python
+        uses: actions/setup-python@v5
+
+      - uses: prefix-dev/setup-pixi@v0.8.14
+        with:
+          pixi-version: "v0.49.0"
+          environments: schedule
+      - name: Run spec_zero_versions.py
+        run: |
+          pixi run -e schedule generate_schedule
+      - name: setup git
+        run: |
+          # git will complain if we don't do this first
+          git config user.name "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+
+      - name: determine tag name
+        id: tag_name
+        run: |
+          echo "TAG_NAME=$(date '+%Y-Q%q')" >> "$GITHUB_OUTPUT"
+
+      - name: Publish github release
+        uses: softprops/action-gh-release@v2
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          generate_release_notes: true
+          tag_name: ${{ steps.tag_name.outputs.TAG_NAME }}
+          make_latest: true
+          files: |
+            schedule.md
+            chart.md
+            schedule.json
diff --git a/.github/workflows/test.yaml b/.github/workflows/test.yaml
new file mode 100644
index 0000000..e926d01
--- /dev/null
+++ b/.github/workflows/test.yaml
@@ -0,0 +1,22 @@
+name: Run the update test suite
+on:
+  push:
+    branches: main
+  pull_request:
+    branches: main
+  # On demand
+  workflow_dispatch:
+
+jobs:
+  run-tests:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - uses: prefix-dev/setup-pixi@v0.8.14
+        with:
+          pixi-version: "v0.49.0"
+          environments: dev
+      - run: |
+          pixi run test
diff --git a/.github/workflows/test_action.yaml b/.github/workflows/test_action.yaml
index 03fb7c1..fd2c7a0 100644
--- a/.github/workflows/test_action.yaml
+++ b/.github/workflows/test_action.yaml
@@ -4,30 +4,14 @@ on: [push, pull_request]
 jobs:
   generate_data:
     runs-on: ubuntu-latest
-    name: Generate version data
+    name: Update test project file
     steps:
       - name: Checkout
         uses: actions/checkout@v5
       - name: Generate version data using local action
         uses: ./
-      - name: Check file contents
-        run: |
-          printf "Contents of chart.md:\n"
-          cat chart.md
-          printf "\n\n"
-          printf "Contents of schedule.json:\n"
-          cat schedule.json
-          printf "\n\n"
-          printf "Contents of schedule.md:\n"
-          cat schedule.md
-          printf "\n\n"
-      - name: Remove generated files
-        run: |
-          printf "Removing generated files...\n"
-          rm -f chart.md schedule.json schedule.md
-          ls -R
-      - uses: actions/download-artifact@v5
-        with:
-          name: spec-zero-versions
-      - name: Display structure of downloaded files
-        run: ls -R
+        with: 
+          project_file_name: tests/test_data/pyproject.toml
+          create_pr: false
+          schedule_path: tests/test_data/test_schedule.json
+
diff --git a/.gitignore b/.gitignore
index d7a22f5..e8f5b39 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,6 @@
 .history
-chart.md
-schedule.md
-schedule.json
+# pixi environments
+.pixi/*
+!.pixi/config.toml
+pixi.lock
+__pycache__
diff --git a/action.yaml b/action.yaml
index ab54c11..1c558dd 100644
--- a/action.yaml
+++ b/action.yaml
@@ -1,26 +1,72 @@
 name: "Generate SPEC-0000 Data"
 description: "Based on the current SPEC 0 schedule, generate a tarball with the latest versions of all packages."
+author: Scientific Python Developers
+inputs:
+  target_branch:
+    description: "Target branch for the pull request"
+    required: true
+    default: "main"
+  project_file_name: 
+    description: "The filename to the project file that lists your dependencies, relative to the repository root. Defaults to 'pyproject.toml' Curretnly only pyproject.toml is supported but others may be added."
+    required: true
+    default: "pyproject.toml"
+  create_pr: 
+    description: "Whether the action should open a PR or not. If this is set to false, this action should have no effect. This is mainly useful for testing"
+    required: true
+    default: true
+  schedule_path:
+    description: "Path to the schedule.json file. If it does not exist yet, it will be downloaded from the spec0-action repository latest release"
+    default: schedule.json
+  token:
+    description: "GitHub token with repo permissions to create pull requests"
+    required: true
 
 runs:
   using: "composite"
   steps:
-    - name: Set up Python
-      uses: actions/setup-python@v5
+    - name: Checkout code
+      uses: actions/checkout@v4
       with:
-        python-version: "3.13"
-    - name: Install dependencies
+        fetch-depth: 0
+
+    - name: Set up Git
+      shell: bash
+      run: |
+        git config user.name "Scientific Python [bot]"
+        git config user.email "scientific-python@users.noreply.github.com"
+
+    - name: Download schedule artifact
       shell: bash
+      env:
+        SCHEDULE_FILE: ${{ inputs.schedule_path }}
       run: |
-        pip install -r requirements.txt
-    - name: Run spec_zero_versions.py
+        if [ ! -f "$SCHEDULE_FILE" ]; then
+          gh release download -R "scientific-python/spec0-action" --pattern schedule.json -O "$SCHEDULE_FILE"
+        fi
+
+    - uses: prefix-dev/setup-pixi@v0.8.14
+      name: Setup pixi
+      with:
+        environments: >-
+          update
+        activate-environment: update
+        pixi-version: v0.49.0
+        manifest-path: ${{github.action_path}}/pyproject.toml
+
+    - name: Run Update script
       shell: bash
       run: |
-        python spec_zero_versions.py
-    - name: Upload files as an artifact
-      uses: actions/upload-artifact@v4
+        python ${{github.action_path}}/spec0-update.py "${{github.workspace}}/${{inputs.project_file_name}}" "${{inputs.schedule_path}}" 
+        # let's cleanup after ourselves so it doesn't end up in the PR
+        rm "${{inputs.schedule_path}}"
+
+    - name: Create Pull Request
+      if: ${{ inputs.create_pr == 'true' }}
+      uses: peter-evans/create-pull-request@v6
       with:
-        name: spec-zero-versions
-        path: |
-          schedule.json
-          schedule.md
-          chart.md
+        token: ${{ inputs.token }}
+        commit-message: "chore: Drop support for unsupported packages conform SPEC 0"
+        title: "Drop support for unsupported packages conform SPEC 0"
+        body: "This PR was created automatically"
+        base: ${{ inputs.target_branch }}
+        branch: update-spec-0-dependencies-${{ github.run_id }}
diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..fb1c998
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,38 @@
+[project]
+authors         = [{ name = "Scientific Python Developers" }]
+name            = "spec0-action"
+requires-python = ">= 3.11"
+version         = "0.1.0"
+dependencies    = ["packaging>=25.0"]
+
+[build-system]
+build-backend = "hatchling.build"
+requires      = ["hatchling"]
+
+[tool.pixi.workspace]
+channels  = ["conda-forge"]
+platforms = ["linux-64"]
+
+[tool.pixi.feature.update.pypi-dependencies]
+spec0-action = { path = ".", editable = true }
+
+[tool.pixi.feature.test.tasks]
+test = { cmd = ["pytest", "-vvv"] }
+
+[tool.pixi.feature.schedule.tasks]
+generate-schedule = { cmd = ["python", "spec0-verions.py"] }
+
+[tool.pixi.feature.test.dependencies]
+pytest = "*"
+
+[tool.pixi.feature.update.dependencies]
+tomlkit = ">=0.13.3,<0.14"
+
+[tool.pixi.feature.schedule.dependencies]
+pandas   = "*"
+requests = "*"
+
+[tool.pixi.environments]
+dev      = ["test", "schedule", "update"]
+schedule = ["schedule"]
+update   = ["update"]
diff --git a/readme.md b/readme.md
index c05545c..e88f013 100644
--- a/readme.md
+++ b/readme.md
@@ -1,63 +1,51 @@
 # SPEC-0 Versions Action
 
-This repository contains a GitHub Action to generate the files required for the SPEC-0 documentation.
+This repository contains a Github Action to update Python dependencies such that they conform to the SPEC 0 support schedule.
+It also contains released versions of the schedule in various formats that that action can use to open PRs in your repository.
 
 ## Using the action
 
+To use the action you can copy the yaml below, and paste it into `.github/workflows/update-spec-0.yaml`.
+The arguments below are filled with their default value, in most cases you won't have to fill them.
+All except for `token` are optional. 
+
+Whenever the action is triggered it will open a PR in your repository that will update the dependencies of SPEC 0 to the new lower bound.
+For this you will have to provide it with a PAT that has write permissions in the `contents` and `pull request` scopes.
+Please refer to the GitHub documentation for instructions on how to do this [here](https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/managing-your-personal-access-tokens).
+
+
 ```yaml
-name: Generate spec-zero data
+name: Update SPEC 0 dependencies
 
 on:
-  push:
-    branches:
-      - main
+  workflow_dispatch:
+  schedule:
+    # At 00:00 on day-of-month 2 in every 3rd month. (i.e. every quarter)
+    # Releases should happen on the first day of the month in scientific-python/spec-zero-tools
+    # so allow one day as a buffer to avoid timing issues
+    - cron: "0 0 2 */3 *"
+
+permissions:
+    contents: write
+    pull-requests: write
 
 jobs:
-  devstats-query:
+    update:
     runs-on: ubuntu-latest
     steps:
-      - uses: scientific-python/spec0-action@main
+      - uses: scientific-python/spec0-action@v1
+    with: 
+        token: ${{ secrets.GH_PAT }}
+        project_file_name: "pyproject.toml"
+        target_branch: 'main'
 ```
 
-The above would produce an artifact named `spec-zero-versions`, the following files: `schedule.yaml`,`schedule.md` and `chart.md`.
-
-To help projects stay compliant with SPEC-0, we provide a `schedule.json` file that can be used by CI systems to determine new version boundaries.
-The structure of the file is as follows:
+It should update any of the packages listed in the `dependency`, or `tool.pixi.*` tables. 
 
-```json
-[
-  {
-    "start_date": "iso8601_timestamp",
-    "packages": {
-      "package_name": "version"
-    }
-  }
-]
-```
+## Limitations
 
-All information in the json file is in a string format that should be easy to use.
-The date is the first timestamp of the relevant quarter.
-Thus a workflow for using this file could be:
+1. Since this action simply parses the toml to do the upgrade and leaves any other bounds intact, it is possible that the environment of the PR becomes unsolvable.
+   For example if you have a numpy dependency like so: `numpy = ">=1.25.0,<2"` this will get updated in the PR to `numpy = "2.0.0,<2"` which is infeasible. 
+   Keeping the resulting environment solvable is outside the scope of this action, so you might have to be adjusted manually.
+2. Currently only `pyproject.toml` is supported by this action, though other manifest files could be considered upon request. 
 
-1. Fetch `schedule.json`
-2. Determine maximum date that is smaller than current date
-3. Update packages listed with new minimum versions
-
-You can obtain the new versions you should set by using this `jq` expression:
-
-```sh
-jq 'map(select(.start_date |fromdateiso8601 |tonumber  < now))| sort_by("start_date") | reverse | .[0].packages ' schedule.json
-```
-
-If you use a package manager like pixi you could update the dependencies with a bash script like this (untested):
-
-```sh
-curl -Ls -o schedule.json https://raw.githubusercontent.com/scientific-python/specs/main/spec-0000/schedule.json
-for line in $(jq 'map(select(.start_date |fromdateiso8601 |tonumber  < now))| sort_by("start_date") | reverse | .[0].packages | to_entries | map(.key + ":" + .value)[]' --raw-output schedule.json); do
-  package=$(echo "$line" | cut -d ':' -f 1)
-  version=$(echo "$line" | cut -d ':' -f 2)
-  if pixi list -x "^$package" &>/dev/null| grep "No packages" -q; then
-    pixi add "$package>=$version";
-  fi
-done
-```
diff --git a/requirements.txt b/requirements.txt
deleted file mode 100644
index ccaba93..0000000
--- a/requirements.txt
+++ /dev/null
@@ -1,3 +0,0 @@
-packaging
-pandas
-requests
diff --git a/schedule.json b/schedule.json
new file mode 100644
index 0000000..c848ede
--- /dev/null
+++ b/schedule.json
@@ -0,0 +1 @@
+[{"packages": {"ipython": "8.8.0", "numpy": "1.25.0", "python": "3.11", "scikit-learn": "1.3.0", "xarray": "2023.1.0"}, "start_date": "2024-10-01T00:00:00Z"}, {"packages": {"ipython": "8.13.0", "matplotlib": "3.8.0", "networkx": "3.1", "scikit-image": "0.21.0", "scipy": "1.11.0", "xarray": "2023.4.0", "zarr": "2.15.0"}, "start_date": "2025-01-01T00:00:00Z"}, {"packages": {"ipython": "8.15.0", "networkx": "3.2", "numpy": "1.26.0", "pandas": "2.1.0", "scikit-image": "0.22.0", "scikit-learn": "1.4.0", "scipy": "1.12.0", "xarray": "2023.7.0", "zarr": "2.16.0"}, "start_date": "2025-04-01T00:00:00Z"}, {"packages": {"ipython": "8.17.0", "matplotlib": "3.9.0", "numpy": "2.0.0", "pandas": "2.2.0", "xarray": "2023.10.0", "zarr": "2.17.0"}, "start_date": "2025-07-01T00:00:00Z"}, {"packages": {"ipython": "8.20.0", "networkx": "3.3", "python": "3.12", "scikit-image": "0.23.0", "xarray": "2024.1.0"}, "start_date": "2025-10-01T00:00:00Z"}, {"packages": {"ipython": "8.24.0", "pandas": "2.3.0", "scikit-learn": "1.5.0", "scipy": "1.13.0", "xarray": "2024.5.0", "zarr": "2.18.0"}, "start_date": "2026-01-01T00:00:00Z"}, {"packages": {"ipython": "8.27.0", "matplotlib": "3.10.0", "networkx": "3.4", "numpy": "2.1.0", "scikit-image": "0.25.0", "scikit-learn": "1.6.0", "scipy": "1.15.0", "xarray": "2024.7.0", "zarr": "3.0.0"}, "start_date": "2026-04-01T00:00:00Z"}, {"packages": {"ipython": "8.28.0", "numpy": "2.2.0", "xarray": "2024.10.0"}, "start_date": "2026-07-01T00:00:00Z"}, {"packages": {"ipython": "8.32.0", "networkx": "3.5", "numpy": "2.3.0", "python": "3.13", "scikit-learn": "1.7.0", "xarray": "2025.1.0"}, "start_date": "2026-10-01T00:00:00Z"}, {"packages": {"ipython": "9.1.0", "scipy": "1.16.0", "xarray": "2025.4.0", "zarr": "3.1.0"}, "start_date": "2027-01-01T00:00:00Z"}, {"packages": {"ipython": "9.4.0", "xarray": "2025.7.0"}, "start_date": "2027-04-01T00:00:00Z"}]
\ No newline at end of file
diff --git a/spec0-update.py b/spec0-update.py
new file mode 100644
index 0000000..5f2fa4b
--- /dev/null
+++ b/spec0-update.py
@@ -0,0 +1,28 @@
+from spec0_action import update_pyproject_toml, read_toml, write_toml, read_schedule
+from pathlib import Path
+from argparse import ArgumentParser
+
+
+if __name__ == '__main__':
+
+    parser = ArgumentParser(
+                        prog='spec_zero_update',
+                        description='A script to update your project dependencies to be in line with the scientific python SPEC 0 support schedule',
+                        )
+
+    parser.add_argument('toml_path', default="pyproject.toml", help="Path to the project file that lists the dependencies. defaults to 'pyproject.toml'.")           
+    parser.add_argument('schedule_path', default="schedule.json", help="Path to the schedule json payload. defaults to 'schedule.json'")           
+
+    args = parser.parse_args()
+
+    toml_path = Path(args.toml_path)
+    schedule_path = Path(args.schedule_path)
+
+    if not toml_path.exists():
+        raise ValueError(f"{toml_path} was supplied as path to project file but it did not exist")
+
+    project_data = read_toml(toml_path)
+    schedule_data = read_schedule(schedule_path)
+    update_pyproject_toml(project_data, schedule_data)
+
+    write_toml(toml_path, project_data)
diff --git a/spec_zero_versions.py b/spec0-versions.py
similarity index 100%
rename from spec_zero_versions.py
rename to spec0-versions.py
diff --git a/spec0_action/__init__.py b/spec0_action/__init__.py
new file mode 100644
index 0000000..5e6eea0
--- /dev/null
+++ b/spec0_action/__init__.py
@@ -0,0 +1,119 @@
+from packaging.specifiers import SpecifierSet
+from typing import Sequence, cast
+import datetime
+
+from spec0_action.versions import repr_spec_set, tighten_lower_bound
+from spec0_action.parsing import (
+    SupportSchedule,
+    Url,
+    is_url_spec,
+    parse_pep_dependency,
+    parse_version_spec,
+    read_schedule,
+    read_toml,
+    write_toml
+)
+from packaging.version import Version
+
+
+__all__ = ["read_schedule", "read_toml", "write_toml", "update_pyproject_toml"]
+
+def update_pyproject_dependencies(dependencies: dict, schedule: SupportSchedule):
+    # Iterate by idx because we want to update it inplace
+    for i in range(len(dependencies)):
+        dep_str = dependencies[i]
+        pkg, extras, spec = parse_pep_dependency(dep_str)
+
+        if isinstance(spec, Url) or pkg not in schedule["packages"]:
+            continue
+
+        new_lower_bound = Version(schedule["packages"][pkg])
+        try:
+            spec = tighten_lower_bound(spec or SpecifierSet(), new_lower_bound)
+            # Will raise a value error if bound is already tighter, in this case we just do nothing and  continue
+        except ValueError:
+            continue
+
+        if not extras:
+            new_dep_str = f"{pkg}{repr_spec_set(spec)}"
+        else:
+            new_dep_str = f"{pkg}{extras}{repr_spec_set(spec)}"
+
+        dependencies[i] = new_dep_str
+
+
+def update_dependency_table(dep_table: dict, new_versions: dict):
+    for pkg, pkg_data in dep_table.items():
+        # Don't do anything for pkgs that aren't in our schedule
+        if pkg not in new_versions:
+            continue
+
+        # Like pkg = ">x.y.z,<a"
+        if isinstance(pkg_data, str):
+            if not is_url_spec(pkg_data):
+                spec = parse_version_spec(pkg_data)
+
+                new_lower_bound = Version(new_versions[pkg])
+                spec = tighten_lower_bound(spec, new_lower_bound)
+
+                dep_table[pkg] = repr_spec_set(spec)
+
+            else:
+                # We don't do anything with url spec dependencies
+                continue
+        else:
+            # Table like in tests = {path = "."}
+            if "path" in pkg_data:
+                # We don't do anything with path dependencies
+                continue
+
+            spec = SpecifierSet(pkg_data["version"])
+            new_lower_bound = Version(new_versions[pkg])
+            spec = tighten_lower_bound(spec, new_lower_bound)
+
+            pkg_data["version"] = repr_spec_set(spec)
+
+
+def update_pixi_dependencies(pixi_tables: dict, schedule: SupportSchedule):
+    if "pypi-dependencies" in pixi_tables: 
+        update_dependency_table(pixi_tables["pypi-dependencies"], schedule["packages"])
+    if "dependencies" in pixi_tables: 
+        update_dependency_table(pixi_tables["dependencies"], schedule["packages"])
+
+    if "feature" in pixi_tables:
+        for _, feature_data in pixi_tables["feature"].items():
+            if "dependencies" in feature_data:
+                update_dependency_table(feature_data["dependencies"], schedule["packages"])
+
+
+def update_pyproject_toml(
+    pyproject_data: dict, schedule_data: Sequence[SupportSchedule]
+):
+    now = datetime.datetime.now(datetime.UTC)
+    try:
+        new_version = cast(
+            SupportSchedule,
+            next(
+                filter(
+                    lambda s: now >= datetime.datetime.fromisoformat(s["start_date"]),
+                    schedule_data,
+                )
+            ),
+        )
+    except StopIteration:
+        raise RuntimeError(
+            "Could not find schedule that applies to current time, perhaps your schedule is oudated."
+        )
+
+    if "python" in new_version["packages"]:
+        pyproject_data["project"]["requires-python"] = repr_spec_set(
+            parse_version_spec(new_version["packages"]["python"])
+        )
+
+    update_pyproject_dependencies(
+        pyproject_data["project"]["dependencies"], new_version
+    )
+
+    if "tool" in pyproject_data and "pixi" in pyproject_data['tool']:
+        pixi_data = pyproject_data["tool"]["pixi"]
+        update_pixi_dependencies(pixi_data, new_version)
diff --git a/spec0_action/parsing.py b/spec0_action/parsing.py
new file mode 100644
index 0000000..096b049
--- /dev/null
+++ b/spec0_action/parsing.py
@@ -0,0 +1,80 @@
+from typing import TypeAlias
+from urllib.parse import ParseResult, urlparse
+from tomlkit import dumps, loads
+import json
+from packaging.specifiers import InvalidSpecifier, SpecifierSet
+from packaging.version import InvalidVersion, Version
+from typing import Dict, Sequence, Tuple, TypedDict
+from pathlib import Path
+from re import compile
+
+# We won't actually do anything with URLs we just need to detect them
+Url: TypeAlias = ParseResult
+
+# Slightly modified version of https://packaging.python.org/en/latest/specifications/dependency-specifiers/#names
+PEP_PACKAGE_IDENT_RE = compile(r"(?im)^([A-Z0-9][A-Z0-9._-]*)(\[[A-Z0-9._,-]+\])?(.*)$")
+
+
+class SupportSchedule(TypedDict):
+    start_date: str
+    packages: Dict[str, str]
+
+
+def parse_version_spec(s: str) -> SpecifierSet:
+    if s.strip() == "*":
+        # Python version numeric components must be non-negative so this is okay
+        # see https://packaging.python.org/en/latest/specifications/version-specifiers/
+        return SpecifierSet(">=0")
+    try:
+        # If we can simply parse it return it
+        return SpecifierSet(s)
+    except InvalidSpecifier:
+        try:
+            ver = Version(s)
+        except InvalidVersion:
+            raise ValueError(f"{s} is not a version or specifyer")
+
+        return SpecifierSet(f">={ver}")
+
+
+def write_toml(path: Path | str, data: dict):
+    with open(path, "w") as file:
+        contents = dumps(data)
+        file.write(contents)
+
+
+def read_toml(path: Path | str) -> dict:
+    with open(path, "r") as file:
+        contents = file.read()
+        return loads(contents)
+
+
+def read_schedule(path: Path | str) -> Sequence[SupportSchedule]:
+    with open(path, "r") as file:
+        return json.load(file)
+
+
+def parse_pep_dependency(dep_str: str) -> Tuple[str, str | None, SpecifierSet | Url | None]:
+    match = PEP_PACKAGE_IDENT_RE.match(dep_str)
+    if match is None:
+        raise ValueError("Could not find any valid python package identifier")
+
+    pkg, extras, spec_str = match.groups()
+
+    extras = extras or None
+
+    if is_url_spec(spec_str):
+        spec = urlparse(spec_str.split("@")[1])
+    elif not spec_str:
+        spec = None
+    else:
+        spec = SpecifierSet(spec_str)
+
+    return (pkg, extras, spec)
+
+
+def is_url_spec(str_spec: str|None) -> bool:
+    if str_spec is None:
+        return False
+
+    return str_spec.strip().startswith("@")
diff --git a/spec0_action/versions.py b/spec0_action/versions.py
new file mode 100644
index 0000000..f88748e
--- /dev/null
+++ b/spec0_action/versions.py
@@ -0,0 +1,28 @@
+from packaging.version import Version
+from packaging.specifiers import Specifier, SpecifierSet
+
+
+def tighten_lower_bound(
+    spec_set: SpecifierSet, new_lower_bound: Version
+) -> SpecifierSet:
+    out = []
+    contains_lower_bound = False
+
+    for spec in spec_set:
+        if spec.operator not in [">", ">="]:
+            out.append(spec)
+            continue
+        if new_lower_bound in spec:
+            out.append(Specifier(f">={new_lower_bound}"))
+            contains_lower_bound = True
+        else:
+            raise ValueError(f"{spec} is already stricter than {new_lower_bound}")
+
+    if not contains_lower_bound:
+        out.append(Specifier(f">={new_lower_bound}"))
+
+    return SpecifierSet(out)
+
+
+def repr_spec_set(spec: SpecifierSet) -> str:
+    return ",".join(sorted(map(str, spec), reverse=True)).replace(" ", "")
diff --git a/tests/test_data/pyproject.toml b/tests/test_data/pyproject.toml
new file mode 100644
index 0000000..8bcee20
--- /dev/null
+++ b/tests/test_data/pyproject.toml
@@ -0,0 +1,29 @@
+[project]
+authors         = [{ name = "Sam Vente", email = "savente93@proton.me" }]
+name            = "tests"
+requires-python = ">=3.10"
+version         = "0.1.0"
+dependencies    = ["ipython>=8.7.0,<4", "numpy[foo,bar]>=1.10.0,<2"]
+
+[build-system]
+build-backend = "hatchling.build"
+requires      = ["hatchling"]
+
+[tool.pixi.workspace]
+channels  = ["conda-forge"]
+platforms = ["linux-64"]
+
+[tool.pixi.pypi-dependencies]
+tests        = { path = ".", editable = true }
+scikit-learn = ">=1.2.0"
+
+[tool.pixi.tasks]
+
+[tool.pixi.feature.foo.dependencies]
+xarray = "*"
+
+[tool.pixi.environments]
+bar = ["foo"]
+
+[tool.pixi.dependencies]
+numpy = ">=1.10.0,<2"
diff --git a/tests/test_data/pyproject_updated.toml b/tests/test_data/pyproject_updated.toml
new file mode 100644
index 0000000..1fee189
--- /dev/null
+++ b/tests/test_data/pyproject_updated.toml
@@ -0,0 +1,29 @@
+[project]
+authors         = [{ name = "Sam Vente", email = "savente93@proton.me" }]
+name            = "tests"
+requires-python = ">=3.11"
+version         = "0.1.0"
+dependencies    = ["ipython>=8.8.0,<4", "numpy[foo,bar]>=1.25.0,<2"]
+
+[build-system]
+build-backend = "hatchling.build"
+requires      = ["hatchling"]
+
+[tool.pixi.workspace]
+channels  = ["conda-forge"]
+platforms = ["linux-64"]
+
+[tool.pixi.pypi-dependencies]
+tests        = { path = ".", editable = true }
+scikit-learn = ">=1.3.0"
+
+[tool.pixi.tasks]
+
+[tool.pixi.feature.foo.dependencies]
+xarray = ">=2023.1.0"
+
+[tool.pixi.environments]
+bar = ["foo"]
+
+[tool.pixi.dependencies]
+numpy = ">=1.25.0,<2"
diff --git a/tests/test_data/test_schedule.json b/tests/test_data/test_schedule.json
new file mode 100644
index 0000000..ec6c35e
--- /dev/null
+++ b/tests/test_data/test_schedule.json
@@ -0,0 +1 @@
+[{"packages": {"ipython": "8.8.0", "numpy": "1.25.0", "python": "3.11", "scikit-learn": "1.3.0", "xarray": "2023.1.0"}, "start_date": "2024-10-01T00:00:00Z"}, {"packages": {"ipython": "8.13.0", "matplotlib": "3.8.0", "networkx": "3.1", "scikit-image": "0.21.0", "scipy": "1.11.0", "xarray": "2023.4.0", "zarr": "2.15.0"}, "start_date": "2025-01-01T00:00:00Z"}, {"packages": {"ipython": "8.15.0", "networkx": "3.2", "numpy": "1.26.0", "pandas": "2.1.0", "scikit-image": "0.22.0", "scikit-learn": "1.4.0", "scipy": "1.12.0", "xarray": "2023.7.0", "zarr": "2.16.0"}, "start_date": "2025-04-01T00:00:00Z"}, {"packages": {"ipython": "8.17.0", "matplotlib": "3.9.0", "numpy": "2.0.0", "pandas": "2.2.0", "xarray": "2023.10.0", "zarr": "2.17.0"}, "start_date": "2025-07-01T00:00:00Z"}, {"packages": {"ipython": "8.20.0", "networkx": "3.3", "python": "3.12", "scikit-image": "0.23.0", "xarray": "2024.1.0"}, "start_date": "2025-10-01T00:00:00Z"}, {"packages": {"ipython": "8.24.0", "pandas": "2.3.0", "scikit-learn": "1.5.0", "scipy": "1.13.0", "xarray": "2024.5.0", "zarr": "2.18.0"}, "start_date": "2026-01-01T00:00:00Z"}, {"packages": {"ipython": "8.27.0", "matplotlib": "3.10.0", "networkx": "3.4", "numpy": "2.1.0", "scikit-image": "0.25.0", "scikit-learn": "1.6.0", "scipy": "1.15.0", "xarray": "2024.7.0", "zarr": "3.0.0"}, "start_date": "2026-04-01T00:00:00Z"}, {"packages": {"ipython": "8.28.0", "numpy": "2.2.0", "xarray": "2024.10.0"}, "start_date": "2026-07-01T00:00:00Z"}, {"packages": {"ipython": "8.32.0", "networkx": "3.5", "numpy": "2.3.0", "python": "3.13", "scikit-learn": "1.7.0", "xarray": "2025.1.0"}, "start_date": "2026-10-01T00:00:00Z"}, {"packages": {"ipython": "9.1.0", "scipy": "1.16.0", "xarray": "2025.4.0", "zarr": "3.1.0"}, "start_date": "2027-01-01T00:00:00Z"}, {"packages": {"ipython": "9.4.0", "xarray": "2025.7.0"}, "start_date": "2027-04-01T00:00:00Z"}]
diff --git a/tests/test_parsing.py b/tests/test_parsing.py
new file mode 100644
index 0000000..c5b23bf
--- /dev/null
+++ b/tests/test_parsing.py
@@ -0,0 +1,65 @@
+from spec0_action.parsing import parse_version_spec, parse_pep_dependency
+from packaging.specifiers import SpecifierSet
+import pytest
+from urllib.parse import urlparse
+
+
+def test_parsing_correct():
+    assert SpecifierSet(">=0") == parse_version_spec("*")
+    assert SpecifierSet(">4,<9") == parse_version_spec(">4, <9")
+    assert SpecifierSet(">=4") == parse_version_spec(">=4")
+    assert SpecifierSet(">=2025.7") == parse_version_spec(">=2025.7")
+
+
+def test_parsing_incorrect():
+    with pytest.raises(ValueError):
+        parse_version_spec("-18")
+
+    with pytest.raises(ValueError):
+        parse_version_spec("asdf")
+
+
+def test_pep_dependency_parsing():
+    matplotlib_str = "matplotlib"
+    pkg, features, spec = parse_pep_dependency(matplotlib_str)
+
+    assert pkg == "matplotlib", pkg
+    assert features is None, features
+    assert spec is None, spec
+
+
+def test_pep_dependency_parsing_with_spec_and_optional_dep():
+    matplotlib_str = "matplotlib[foo,bar]>=3.7.0,<4"
+    pkg, features, spec = parse_pep_dependency(matplotlib_str)
+
+    assert pkg == "matplotlib", pkg
+    assert features == "[foo,bar]", features
+    assert spec == SpecifierSet(">=3.7.0,<4"), spec
+
+def test_pep_dependency_parsing_with_spec():
+    matplotlib_str = "matplotlib>=3.7.0,<4"
+    pkg, features, spec = parse_pep_dependency(matplotlib_str)
+
+    assert pkg == "matplotlib", pkg
+    assert features is None, features
+    assert spec == SpecifierSet(">=3.7.0,<4"), spec
+
+
+def test_pep_dependency_parsing_with_url_spec():
+    dep_str = "matplotlib @ https://github.com/pypa/pip/archive/1.3.1.zip#sha1=da9234ee9982d4bbb3c72346a6de940a148ea686"
+    pkg, features, spec = parse_pep_dependency(dep_str)
+
+    assert pkg == "matplotlib", pkg
+    assert features is None, features
+    assert spec == urlparse(
+        " https://github.com/pypa/pip/archive/1.3.1.zip#sha1=da9234ee9982d4bbb3c72346a6de940a148ea686"
+    ), spec
+
+
+def test_pep_dependency_parsing_extra_restrictions():
+    matplotlib_str = "matplotlib>=3.7.0,<4,!=3.8.14"
+    pkg, features, spec = parse_pep_dependency(matplotlib_str)
+
+    assert pkg == "matplotlib", pkg
+    assert features is None, features
+    assert spec == SpecifierSet("!=3.8.14,<4,>=3.7.0"), spec
diff --git a/tests/test_update_pyproject_toml.py b/tests/test_update_pyproject_toml.py
new file mode 100644
index 0000000..40397fb
--- /dev/null
+++ b/tests/test_update_pyproject_toml.py
@@ -0,0 +1,11 @@
+from spec0_action.parsing import read_schedule, read_toml
+from spec0_action import update_pyproject_toml
+
+
+def test_update_pyproject_toml():
+    expected = read_toml("tests/test_data/pyproject_updated.toml")
+    pyproject_data = read_toml("tests/test_data/pyproject.toml")
+    test_schedule = read_schedule("tests/test_data/test_schedule.json")
+    update_pyproject_toml(pyproject_data, test_schedule)
+
+    assert pyproject_data == expected
diff --git a/tests/test_versions.py b/tests/test_versions.py
new file mode 100644
index 0000000..e364f7b
--- /dev/null
+++ b/tests/test_versions.py
@@ -0,0 +1,29 @@
+from packaging.version import Version
+from spec0_action.versions import repr_spec_set, tighten_lower_bound
+from packaging.specifiers import SpecifierSet
+
+
+def test_repr_specset():
+    spec = SpecifierSet("<7,!=3.8.0,>4,~=3.14")
+    assert repr_spec_set(spec) == "~=3.14,>4,<7,!=3.8.0"
+
+
+def test_tighter_lower_bound_any():
+    spec = SpecifierSet(">=0")
+    lower_bound = Version("3.8.0")
+    tightened = tighten_lower_bound(spec, lower_bound)
+    assert tightened == SpecifierSet(">=3.8.0")
+
+
+def test_tighter_lower_bound_leaves_other_restrictions():
+    spec = SpecifierSet("~= 0.9,>=1.0,!= 1.3.4.*,< 2.0")
+    lower_bound = Version("3.8.0")
+    tightened = tighten_lower_bound(spec, lower_bound)
+    assert tightened == SpecifierSet("~= 0.9,>=3.8.0,!=1.3.4.*,<2.0")
+
+
+def test_tighter_lower_bound_adds_lower_bound_if_not_present():
+    spec = SpecifierSet("~=0.9,!=1.3.4.*,<2.0")
+    lower_bound = Version("3.8.0")
+    tightened = tighten_lower_bound(spec, lower_bound)
+    assert tightened == SpecifierSet("~= 0.9,  != 1.3.4.*, < 2.0, >=3.8.0")