Haystack

Haystack is a powerful search tool that indexes your open VS Code project in the background, enabling fast and efficient code search — ideal for large codebases like Chromium.

Prerequisites

• You must have a VSCode workspace opened to the src\ folder of the Chromium repository.

Setup Instructions

1. Install the Haystack Search Extension

   • In VS Code, click this link and install Haystack Search from the Marketplace.
   • Continue with other steps while waiting for the indexing process to complete (approximately 15 minutes for the Chromium codebase).

2. Add MCP Server

   • Run the MCP: Add Server… command in VS Code.
   • Select “HTTP (server-sent events)”.
   • Enter http://localhost:13135/mcp/sse as the server URL.
   • Provide a name (ex: “haystack-search”).
   • Choose “Workspace Settings” as the scope.

3. Enable Agent Mode

   • Switch GitHub Copilot to Agent mode using the UX dropdown to benefit from Haystack.

4. Activate Haystack Agent Mode Prompt in various ways

   • Use the paperclip icon to Add Context... -> Instructions -> chromium_haystack
   • Configure for automatic inclusion using create user instructions
   • Use the keyboard shortcut option+command+/ on MacOS or ctrl+alt+/ on Windows -> Haystack.
   • Use the instruction shortcut with # -> #haystack.instructions.md

5. Start Coding

   • Enjoy an enhanced GitHub Copilot experience in the Chromium repository.