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+# Contributing to Codeplain
+
+Thanks for contributing to Codeplain.
+
+## Before You Start
+
+Check existing issues and pull requests before starting work.
+
+Keep each contribution focused on one issue or a closely related set of changes.
+
+## Contribution Workflow
+
+1. Fork the Codeplain repository.
+2. Make your changes on a branch in your fork.
+3. Commit and push the changes to your fork.
+4. Open a pull request against the Codeplain `main` branch.
+
+## Configure Codeplain
+
+Use your own Codeplain API key for local development and testing.
+
+Never commit API keys, credentials, or other secrets.
+
+## Test with a Plain Example
+
+When relevant, test your change with an existing example from the `plainlang-examples` repository.
+
+This provides a real `.plain` project for verifying the change in an actual Codeplain workflow.
+
+## Run Tests
+
+Run the tests relevant to your change before opening a pull request.
+
+For changes that affect the CLI, rendering, or test execution, also test the change by running the relevant Codeplain command from the terminal.
+
+Check that:
+
+* the command returns the expected exit code,
+* errors are clear and do not expose unintended tracebacks,
+* existing Codeplain behavior still works.
+
+For platform-specific changes, test the relevant `.sh` or `.ps1` workflow.
+
+## Keep the Change Clean
+
+Before submitting:
+
+* remove temporary files and debugging output,
+* avoid unrelated changes,
+* add or update tests where needed,
+* update documentation when behavior changes,
+* verify that no secrets are included.
+
+Review your changes with:
+
+```bash
+git status
+git diff
+```
+
+## Pull Request
+
+Include:
+
+* what changed,
+* why it changed,
+* the related issue, when applicable,
+* how the change was tested,
+* the `plainlang-examples` example used, when relevant.