core/.github/copilot-instructions.md

Copilot code review instructions

• Start review comments with a short, one-sentence summary of the suggested fix.
• Do not comment on code style, formatting or linting issues.
• A Pull Request with a dependency version bump should only contain changes required for the version bump. If the PR includes other changes, request that they are removed from the PR.

GitHub Copilot & Claude Code Instructions

This repository contains the core of Home Assistant, a Python 3 based home automation application.

Git Commit Guidelines

• Do NOT amend, squash, or rebase commits that have already been pushed to the PR branch after the PR is opened - Reviewers need to follow the commit history, as well as see what changed since their last review

Pull Requests

• When opening a pull request, use the repository's PR template (.github/PULL_REQUEST_TEMPLATE.md). NEVER REMOVE ANYTHING from the template.
• Do not remove checkboxes that are not checked — leave all unchecked checkboxes in place so reviewers can see which options were not selected.

Development Commands

• When entering a new environment or worktree, run script/setup to set up the virtual environment with all development dependencies (pylint, pre-commit hooks, etc.). This is required before committing.
• .vscode/tasks.json contains useful commands used for development.

Python Syntax Notes

• Home Assistant officially supports Python 3.14 as its minimum version. Do not flag syntax or features that require Python 3.14 as issues, and do not suggest workarounds for older Python versions.
• Python 3.14 explicitly allows except TypeA, TypeB: without parentheses. Never flag this as an issue.
• Python 3.14 evaluates annotations lazily (PEP 649). Forward references in annotations do not need to be quoted — annotations can reference names defined later in the module without quoting them or using from __future__ import annotations. Do not flag unquoted forward references in annotations as issues.

Testing

• Use uv run pytest to run tests
• After modifying strings.json for an integration, regenerate the English translation file before running tests: .venv/bin/python3 -m script.translations develop --integration <integration_name>. Tests load translations from the generated translations/en.json, not directly from strings.json.
• When writing or modifying tests, ensure all test function parameters have type annotations.
• Prefer concrete types (for example, HomeAssistant, MockConfigEntry, etc.) over Any.
• Prefer @pytest.mark.usefixtures over arguments, if the argument is not going to be used.
• Avoid using conditions/branching in tests. Instead, either split tests or adjust the test parametrization to cover all cases without branching.
• If multiple tests share most of their code, use pytest.mark.parametrize to merge them into a single parameterized test instead of duplicating the body. Use pytest.param with an id parameter to name the test cases clearly.
• We use Syrupy for snapshot testing. Leverage .ambr snapshots instead of repetitive and exhaustive generation of test data within Python code itself.

Good practices

• Integrations with Platinum or Gold level in the Integration Quality Scale reflect a high standard of code quality and maintainability. When looking for examples of something, these are good places to start. The level is indicated in the manifest.json of the integration.
• When reviewing entity actions, do not suggest extra defensive checks for input fields that are already validated by Home Assistant's service/action schemas and entity selection filters. Suggest additional guards only when data bypasses those validators or is transformed into a less-safe form.
• When validation guarantees a dict key exists, prefer direct key access (data["key"]) instead of .get("key") so contract violations are surfaced instead of silently masked.
• Do not add comments that just restate the code on the following line(s) (e.g. # Check if initialized above if self.initialized:). Comments should only explain why — non-obvious constraints, surprising behavior, or workarounds — never what.