diff --git a/AGENTS.md b/AGENTS.md
new file mode 100644
index 00000000..798417b7
--- /dev/null
+++ b/AGENTS.md
@@ -0,0 +1,341 @@
+# AGENTS.md
+
+This file provides guidance for AI coding agents working on the **MyST-Parser** repository.
+
+## Project Overview
+
+MyST-Parser is a Sphinx extension and docutils parser for the MyST (Markedly Structured Text) Markdown flavor. It provides:
+
+- An extended [CommonMark](https://commonmark.org)-compliant parser using [`markdown-it-py`](https://markdown-it-py.readthedocs.io/)
+- A [docutils](https://docutils.sourceforge.io/) renderer that converts markdown-it tokens to docutils nodes
+- A [Sphinx](https://www.sphinx-doc.org) extension for using MyST Markdown in Sphinx documentation
+
+MyST is designed for technical documentation and publishing, offering a rich and extensible flavor of Markdown with support for roles, directives, and cross-references.
+
+## Repository Structure
+
+```
+pyproject.toml          # Project configuration and dependencies
+tox.ini                 # Tox test environment configuration
+
+myst_parser/            # Main source code
+├── __init__.py         # Package init with Sphinx setup() entry point
+├── config/             # Configuration dataclasses
+│   ├── main.py         # MdParserConfig dataclass
+│   └── dc_validators.py # Dataclass field validators
+├── parsers/            # Parser implementations
+│   ├── sphinx_.py      # Sphinx parser (MystParser)
+│   ├── docutils_.py    # Docutils parser and CLI tools
+│   ├── mdit.py         # markdown-it-py setup and plugins
+│   ├── directives.py   # Directive parsing utilities
+│   └── options.py      # Option parsing for directives
+├── mdit_to_docutils/   # Token-to-docutils rendering
+│   ├── base.py         # DocutilsRenderer (main renderer)
+│   ├── sphinx_.py      # SphinxRenderer (Sphinx-specific)
+│   ├── transforms.py   # Docutils transforms
+│   └── html_to_nodes.py # HTML-to-docutils conversion
+├── sphinx_ext/         # Sphinx extension components
+│   ├── main.py         # setup_sphinx() and config creation
+│   ├── directives.py   # Custom Sphinx directives
+│   ├── myst_refs.py    # Reference resolver post-transform
+│   └── mathjax.py      # MathJax configuration
+├── inventory.py        # Sphinx inventory file handling
+├── mocking.py          # Mock objects for directive/role parsing
+├── warnings_.py        # Warning types (MystWarnings enum)
+├── cli.py              # Command-line interface
+└── _compat.py          # Python version compatibility
+
+tests/                  # Test suite
+├── test_sphinx/        # Sphinx integration tests
+│   ├── sourcedirs/     # Test documentation projects
+│   └── test_sphinx_builds.py
+├── test_renderers/     # Renderer unit tests
+├── test_commonmark/    # CommonMark compliance tests
+├── test_html/          # HTML output tests
+├── test_docutils.py    # Docutils parser tests
+└── test_anchors.py     # Heading anchor tests
+
+docs/                   # Documentation source (MyST Markdown)
+├── conf.py             # Sphinx configuration
+├── index.md            # Documentation index
+├── syntax/             # Syntax reference documentation
+├── develop/            # Developer documentation
+└── faq/                # FAQ and troubleshooting
+```
+
+## Development Commands
+
+All commands should be run via [`tox`](https://tox.wiki) for consistency. The project uses `tox-uv` for faster environment creation.
+
+### Testing
+
+```bash
+# Run all tests
+tox
+
+# Run a specific test file
+tox -- tests/test_docutils.py
+
+# Run a specific test function
+tox -- tests/test_docutils.py::test_function_name
+
+# Run tests with a specific Python/Sphinx version
+tox -e py311-sphinx8
+
+# Run with coverage
+tox -- --cov=myst_parser
+
+# Update regression test fixtures
+tox -- --regen-file-failure --force-regen
+```
+
+### Documentation
+
+```bash
+# Build docs (clean)
+tox -e docs-clean
+
+# Build docs (incremental)
+tox -e docs-update
+
+# Build with a specific builder (e.g., linkcheck)
+BUILDER=linkcheck tox -e docs-update
+```
+
+### Code Quality
+
+```bash
+# Type checking with mypy
+tox -e mypy
+
+# Linting with ruff (auto-fix enabled)
+tox -e ruff-check
+
+# Formatting with ruff
+tox -e ruff-fmt
+
+# Run pre-commit hooks on all files
+pre-commit run --all-files
+```
+
+## Code Style Guidelines
+
+- **Formatter/Linter**: Ruff (configured in `pyproject.toml`)
+- **Type Checking**: Mypy with strict settings (configured in `pyproject.toml`)
+- **Pre-commit**: Use pre-commit hooks for consistent code style
+
+### Best Practices
+
+- **Type annotations**: Use complete type annotations for all function signatures. Use `TypedDict` for structured dictionaries, dataclasses for configuration.
+- **Docstrings**: Use Sphinx-style docstrings (`:param:`, `:return:`, `:raises:`). Types are not required in docstrings as they should be in type hints.
+- **Function Signatures**: Use `/` and `*` to enforce positional-only and keyword-only arguments where appropriate
+- **Pure functions**: Where possible, write pure functions without side effects.
+- **Error handling**: Use `MystWarnings` enum for warning types. Use `create_warning()` for user-facing warnings.
+- **Testing**: Write tests for all new functionality. Use `pytest-regressions` for output comparison tests.
+
+### Docstring Example
+
+```python
+def parse_directive_text(
+    directive_class: type[Directive],
+    first_line: str,
+    content: str,
+    *,
+    validate_options: bool = True,
+) -> tuple[list[str], dict[str, Any], list[str], int]:
+    """Parse directive text into its components.
+
+    :param directive_class: The directive class to parse for.
+    :param first_line: The first line (arguments).
+    :param content: The directive content.
+    :param validate_options: Whether to validate options against the directive spec.
+    :return: Tuple of (arguments, options, body_lines, body_offset).
+    :raises MarkupError: If the directive text is malformed.
+    """
+    ...
+```
+
+## Testing Guidelines
+
+### Test Structure
+
+- Tests use `pytest` with fixtures from `conftest.py` files
+- Sphinx integration tests are in `tests/test_sphinx/`
+- Test source directories are in `tests/test_sphinx/sourcedirs/`
+- Regression testing uses `pytest-regressions` for output comparison
+- Use `pytest-param-files` for parameterized file-based tests
+
+### Writing Tests
+
+1. For Sphinx integration tests, create a source directory in `tests/test_sphinx/sourcedirs/`
+2. Use `sphinx-pytest` fixtures for Sphinx application testing
+3. Use `file_regression` fixture for comparing output against stored fixtures
+
+### Test Best Practices
+
+- **Test coverage**: Write tests for all new functionality and bug fixes
+- **Isolation**: Each test should be independent and not rely on state from other tests
+- **Descriptive names**: Test function names should describe what is being tested
+- **Regression testing**: Use `file_regression.check()` for complex output comparisons
+- **Parametrization**: Use `@pytest.mark.parametrize` for multiple test scenarios
+- **Fixtures**: Define reusable fixtures in `conftest.py`
+
+### Example Test Pattern
+
+```python
+import pytest
+
+@pytest.mark.sphinx(
+    buildername="html",
+    srcdir="path/to/sourcedir",
+)
+def test_example(app, status, warning, get_sphinx_app_output):
+    app.build()
+    assert "build succeeded" in status.getvalue()
+    warnings = warning.getvalue().strip()
+    assert warnings == ""
+```
+
+## Pull Request Requirements
+
+When submitting changes:
+
+1. **Description**: Include a meaningful description or link explaining the change
+2. **Tests**: Include test cases for new functionality or bug fixes
+3. **Documentation**: Update docs if behavior changes or new features are added
+4. **Changelog**: Update `CHANGELOG.md` under the appropriate section
+5. **Code Quality**: Ensure `pre-commit run --all-files` passes
+
+## Architecture Overview
+
+### Parsing Pipeline
+
+The MyST parser follows a three-stage pipeline:
+
+```
+MyST Markdown → markdown-it tokens → docutils AST → Sphinx/HTML output
+```
+
+1. **Markdown Parsing** (`myst_parser/parsers/mdit.py`): Uses `markdown-it-py` with MyST plugins to parse Markdown into tokens
+2. **Token Rendering** (`myst_parser/mdit_to_docutils/`): Converts markdown-it tokens to docutils nodes
+3. **Sphinx Integration** (`myst_parser/sphinx_ext/`): Integrates with Sphinx for documentation builds
+
+### Key Components
+
+#### Configuration (`myst_parser/config/main.py`)
+
+The `MdParserConfig` dataclass centralizes all MyST configuration options:
+
+- Defines all `myst_*` configuration values with types and defaults
+- Uses dataclass validators for type checking
+- Sphinx config values are auto-registered with `myst_` prefix
+
+#### Parsers (`myst_parser/parsers/`)
+
+- `MystParser` (in `sphinx_.py`): The Sphinx parser class that integrates with Sphinx's build system
+- `Parser` (in `docutils_.py`): The standalone docutils parser for non-Sphinx use
+- `create_md_parser()` (in `mdit.py`): Factory function to create configured markdown-it-py instances
+
+#### Renderers (`myst_parser/mdit_to_docutils/`)
+
+- `DocutilsRenderer` (in `base.py`): Base renderer that converts tokens to docutils nodes. Contains render methods for each token type (e.g., `render_heading`, `render_paragraph`).
+- `SphinxRenderer` (in `sphinx_.py`): Extends `DocutilsRenderer` with Sphinx-specific functionality (e.g., cross-references, domains).
+
+#### Sphinx Extension (`myst_parser/sphinx_ext/`)
+
+- `setup_sphinx()` (in `main.py`): Registers the parser, config values, and transforms with Sphinx
+- `MystReferenceResolver` (in `myst_refs.py`): Post-transform that resolves MyST-style references
+- Custom directives like `figure-md` (in `directives.py`)
+
+### Sphinx Integration Flow
+
+```mermaid
+flowchart TB
+    subgraph init["Initialization"]
+        setup["setup() in __init__.py"]
+        setup_sphinx["setup_sphinx()"]
+    end
+
+    subgraph config["Configuration"]
+        builder_init["builder-inited"]
+        create_config["create_myst_config()"]
+    end
+
+    subgraph parse["Parse Phase"]
+        source["Source .md file"]
+        mdit["markdown-it-py parser"]
+        tokens["Token stream"]
+        renderer["DocutilsRenderer/SphinxRenderer"]
+        doctree["Docutils doctree"]
+    end
+
+    subgraph resolve["Resolution Phase"]
+        post_transform["MystReferenceResolver"]
+        resolved["Resolved doctree"]
+    end
+
+    setup --> setup_sphinx
+    setup_sphinx --> builder_init
+    builder_init --> create_config
+
+    source --> mdit --> tokens --> renderer --> doctree
+    doctree --> post_transform --> resolved
+
+    create_config -.->|"MdParserConfig"| renderer
+
+    style create_config fill:#e1f5fe
+    style renderer fill:#e1f5fe
+    style post_transform fill:#e1f5fe
+```
+
+## Key Files
+
+- `pyproject.toml` - Project configuration, dependencies, and tool settings
+- `myst_parser/__init__.py` - Package entry point with `setup()` for Sphinx
+- `myst_parser/config/main.py` - `MdParserConfig` dataclass with all configuration options
+- `myst_parser/parsers/sphinx_.py` - `MystParser` class for Sphinx integration
+- `myst_parser/mdit_to_docutils/base.py` - `DocutilsRenderer` with token-to-node rendering
+- `myst_parser/sphinx_ext/main.py` - `setup_sphinx()` function for Sphinx setup
+- `myst_parser/warnings_.py` - `MystWarnings` enum for warning types
+
+## Debugging
+
+- Build docs with `-T` flag for full tracebacks: `tox -e docs-clean --  -T ...`
+- Use `myst-docutils-html` CLI for standalone parsing without Sphinx
+- Check `docs/_build/` for build outputs
+- Use `tox -- -v --tb=long` for verbose test output with full tracebacks
+- Set `myst_debug_match = True` in Sphinx config to log matched syntax
+
+## Common Patterns
+
+### Adding a New Syntax Extension
+
+1. Create a markdown-it-py plugin or use an existing one from `mdit-py-plugins`
+2. Register it in `myst_parser/parsers/mdit.py`
+3. Add configuration option in `MdParserConfig` if needed
+4. Add render method in `DocutilsRenderer` (e.g., `render_my_syntax`)
+5. Document in `docs/syntax/`
+6. Add tests in `tests/`
+
+### Adding a Configuration Option
+
+1. Add field to `MdParserConfig` in `myst_parser/config/main.py`
+2. Add validator if needed in `myst_parser/config/dc_validators.py`
+3. Document in `docs/configuration.md`
+4. Add tests for the new option
+
+### Adding a Sphinx Directive
+
+1. Create directive class in `myst_parser/sphinx_ext/directives.py`
+2. Register in `setup_sphinx()` in `myst_parser/sphinx_ext/main.py`
+3. Document in appropriate docs section
+4. Add tests in `tests/test_sphinx/`
+
+## Reference Documentation
+
+- [markdown-it-py Repository](https://github.com/ExecutableBookProject/markdown-it-py)
+- [markdown-it-py Documentation](https://markdown-it-py.readthedocs.io/)
+- [Docutils Repository](https://github.com/live-clones/docutils)
+- [Docutils Documentation](https://docutils.sourceforge.io/)
+- [Sphinx Repository](https://github.com/sphinx-doc/sphinx)
+- [Sphinx Extension Development](https://www.sphinx-doc.org/en/master/extdev/index.html)
diff --git a/pyproject.toml b/pyproject.toml
index c2ffb213..db73c7e3 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -83,6 +83,16 @@ testing-docutils = [
     "pytest-param-files~=0.6.0",
 ]
 
+[dependency-groups]
+mypy = [
+    "mypy==1.19.1",
+    "types-urllib3",
+    "sphinx~=8.2",
+    "markdown-it-py~=4.0",
+    "mdit-py-plugins~=0.5.0",
+]
+ruff = ["ruff==0.14.11"]
+
 [project.scripts]
 myst-anchors = "myst_parser.cli:print_anchors"
 myst-inv = "myst_parser.inventory:inventory_cli"
diff --git a/tox.ini b/tox.ini
index cd87af04..cad8fc7f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -48,3 +48,15 @@ commands =
         --re-ignore _build/.* \
         --port 0 --open-browser \
         -n -b {posargs:html} docs/ docs/_build/{posargs:html}
+
+[testenv:ruff-check]
+dependency_groups = ruff
+commands = ruff check {posargs:--fix}
+
+[testenv:ruff-fmt]
+dependency_groups = ruff
+commands = ruff format {posargs}
+
+[testenv:mypy]
+dependency_groups = mypy
+commands = mypy {posargs:myst_parser}