VS Code Development & Agent Customization

Act on user feedback attached to the current session. Use when the user submits feedback on the session's changes via the Submit Feedback button.

Use when adding, modifying, or reviewing VS Code configuration policies. Covers the full policy lifecycle from registration to export to platform-specific artifacts. Run on ANY change that adds a policy: field to a configuration property.

Create, update, review, fix, or debug VS Code agent customization files (.instructions.md, .prompt.md, .agent.md, SKILL.md, copilot-instructions.md, AGENTS.md). Use for: saving coding preferences; troubleshooting why instructions/skills/agents are ignored or not invoked; configuring applyTo patterns; defining tool restrictions; creating custom agent modes or specialized workflows; packaging domain knowledge; fixing YAML frontmatter syntax.

Run agent-driven VS Code performance or memory investigations. Use when asked to launch Code OSS, automate a VS Code scenario, run the Chat memory smoke runner, capture renderer heap snapshots, take workflow screenshots, compare run summaries, or drive a repeatable scenario before heap-snapshot analysis.

Use when working on the Chat Customizations editor — the management UI for agents, skills, instructions, hooks, prompts, MCP servers, and plugins.

Run chat perf benchmarks and memory leak checks against the local dev build or any published VS Code version. Use when investigating chat rendering regressions, validating perf-sensitive changes to chat UI, or checking for memory leaks in the chat response pipeline.

Analyze V8/Chrome CPU profiles (.cpuprofile) and DevTools trace files (Trace-.json). Use when: profiling performance, investigating slow functions, comparing code paths, finding bottlenecks, analyzing timeToRequest, understanding call trees from sampling profiler data, analyzing layout/paint/rendering, investigating user timing marks.

Create a draft pull request for the current session. Use when the user wants to open a draft PR with the session's changes.

Create an instructions file (.instructions.md) for a project rule or convention.

Generate or modify run commands for the current session. Use when the user wants to set up or update run commands that appear in the session's Run button.

Analyze V8 heap snapshots to investigate memory leaks and retention issues. Use when given .heapsnapshot files, asked to compare before/after snapshots, asked to find what retains objects, or investigating why objects survive GC. Provides snapshot parsing, comparison, retainer-path helpers, and scratchpad scripts.

Use when making code changes to ensure they pass VS Code's hygiene checks. Covers the pre-commit hook, unicode restrictions, string quoting rules, copyright headers, indentation, formatting, ESLint, and stylelint. Run the hygiene check before declaring work complete.

How to install a VS Code extension from an extension ID. Useful when the user wants to add new capabilities to their VS Code environment by installing extensions.

Comprehensive setup steps to help the user create complete project structures in a VS Code workspace; this tool is designed for full project initialization and scaffolding, not for creating individual files. When to use this tool: user wants to create a new complete project from scratch; setting up entire project frameworks (TypeScript projects, React apps, Node.js servers, etc.); initializing Model Context Protocol (MCP) servers with full structure; creating VS Code extensions with proper scaffolding; setting up Next.js, Vite, or other framework-based projects; user asks for "new project", "create a workspace", "set up a [framework] project"; need to establish a complete development environment with dependencies, config files, and folder structure. When NOT to use this tool: creating single files or small code snippets; adding individual files to existing projects; making modifications to existing codebases; user asks to "create a file" or "add a component"; simple code examples or demonstrations; debugging or fixing existing code. This tool provides complete project setup including: folder structure creation; package.json and dependency management; configuration files (tsconfig, eslint, etc.); initial boilerplate code; development environment setup; build and run instructions. Use other file creation tools for individual files within existing projects.

Ensure renamed built-in tool references preserve backward compatibility. Use when renaming a toolReferenceName, tool set referenceName, or any tool identifier. Run on ANY change to tool registration code. Covers legacyToolReferenceFullNames for tools and legacyFullNames for tool sets.

Use when running unit tests in the VS Code repo. Covers the runTests tool, scripts/test.sh (macOS/Linux) and scripts/test.bat (Windows), and their supported arguments for filtering, globbing, and debugging tests.

Create or update repository skills and instructions when major learnings are discovered during a session. Use when the user says "learn!", when a significant pattern or pitfall is identified, or when reusable domain knowledge should be captured for future sessions.

Use when the user wants to run the vscode.dev server locally and exercise the VS Code workbench or Agents window in the integrated browser against the local microsoft/vscode sources. Covers starting the dev server, the vscode-quality=dev URL, browser-driven interaction patterns, and optionally wiring up a local mock agent host for the Agents window.