streamlit

**[REQUIRED]** Use for ALL Streamlit tasks: creating, editing, debugging, beautifying, styling, theming, or optimizing Streamlit applications. Also required for building custom components (inline or packaged), using st.components.v2, or any HTML/JS/CSS component work. Triggers: streamlit, st., dashboard, app.py, beautify, style, CSS, color, background, theme, button, widget styling, custom component, st.components, packaged component, pyproject.toml, asset_dir, CCv2, HTML/JS component.

Explains Streamlit's internal architecture including backend runtime, frontend rendering, and WebSocket communication. Use when debugging cross-layer issues, understanding how features work end-to-end, planning architectural changes, or onboarding to the codebase. Covers ForwardMsg/BackMsg protocol, script rerun model, element tree, widget state management, and more.

Review internal documentation (*.md files) against the current codebase state and propose updates for outdated or incorrect information.

Uploads agent-generated artifacts (specs, plans, learnings) to the streamlit.wiki for sharing via PR comments. Use when you have agent artifacts to share with reviewers.

Diagnose and fix flaky Playwright e2e tests. Use when tests fail intermittently, show timeout errors, have snapshot mismatches, or exhibit browser-specific failures.

Generates polished website release notes between two git tags for docs.streamlit.io. Use when preparing a new Streamlit release or reviewing changes between versions.

Implement a feature from a product/tech spec, URL, or GitHub issue. Reads the spec, implements the feature following Streamlit patterns, and creates a merge-ready PR. Use when given a spec folder path, document URL, or issue link to implement.

Finalizes branch changes for merging by simplifying code, running checks, reviewing changes, and creating a PR if needed. Use when ready to merge changes into the target branch.

Address all valid review comments on a PR for the current branch in the streamlit/streamlit repo. Covers both inline review comments and general PR (issue) comments. Use when a PR has reviewer feedback to address, including code changes, style fixes, and documentation updates.

Assesses whether branch or PR changes are high-risk for externally hosted or embedded Streamlit usage and recommends whether external e2e coverage with `@pytest.mark.external_test` is needed. Use during code review, PR triage, or test planning when changes touch routing, auth, websocket/session behavior, embedding, assets, cross-origin behavior, SiS/Snowflake runtime, storage, or security headers.

Runs Python unit tests with coverage, analyzes coverage reports, and implements meaningful tests to increase coverage by ~0.2%. Use when you want to systematically improve Python test coverage with high-value test cases.

Runs frontend unit tests with coverage, analyzes coverage reports, and implements meaningful tests to increase coverage by ~0.2%. Use when you want to systematically improve frontend test coverage with high-value test cases.

Writes product and tech specs for new Streamlit features. Use when designing new API commands, widgets, or significant changes that need team review before implementation.

Lists available make commands for Streamlit development. Use for build, test, lint, or format tasks.

Validates all code changes before committing by running format, lint, type, and unit test checks. Use after making backend (Python) or frontend (TypeScript) changes, before committing or finishing a work session.

Creates a draft pull request on GitHub with proper labels, branch naming, and description formatting. Use when changes are ready to be submitted as a PR to the streamlit/streamlit repository.

Debug Streamlit frontend and backend changes using make debug with hot-reload. Use when testing code changes, investigating bugs, checking UI behavior, or needing screenshots of the running app.

Analyze and fix failed GitHub Actions CI jobs for the current branch/PR. Use when CI checks fail, PR checks show failures, or you need to diagnose lint/type/test errors and verify fixes locally.