`eslint-docgen` is a developer‑tool that automatically creates Markdown documentation for custom ESLint plugins by extracting rule metadata and the examples defined in `RuleTester` test suites. It replaces the standard `RuleTester` with a wrapper, reads a simple configuration file, and when the test suite is run with `DOCGEN=1` it generates rule docs (including description, deprecation notices, valid/invalid code snippets, fix examples, and source links) and can also build a README index, making it useful for maintainers of ESLint plugins who want to keep their rule documentation in sync with their code and tests.