New Feature Implementation Guide

For understanding the underlying architecture (backend runtime, frontend rendering, WebSocket communication, element tree), see the understanding-streamlit-architecture skill.

Most features need implementation in three areas:

• Backend: lib/streamlit/
• Frontend: frontend/
• Protobufs: proto/

New features should include:

• Python unit tests in lib/tests
• Vitest unit tests
• E2E Playwright tests in e2e_playwright/

Order of Implementation

1. Protobuf changes in proto/ then run make protobuf
   • New elements: add to proto/streamlit/proto/Element.proto