🥦 Broccoli — AI Debugger for VS Code

Broccoli turns "the agent reads a stack trace and guesses" into "the agent drives the real debugger": it sets breakpoints, steps, inspects live variables over the Debug Adapter Protocol, and proposes a fix you approve in a diff — never applied silently.

Two ways to use it:

1. Built-in agent — bring your own API key (Anthropic, OpenAI, Groq, DeepSeek, Together, xAI, Ollama, or any OpenAI-compatible endpoint) and debug from the sidebar.

2. MCP server — expose the same debugger tools over a localhost Model Context Protocol endpoint so external agents like Claude Code or Cursor can debug through your editor.

Quick start (built-in agent)

1. Open the Broccoli icon in the activity bar.

2. Click configure and pick a provider + model (the key is stored in VS Code's SecretStorage, never on disk).

3. Make sure your workspace has a launch.json debug configuration.

4. Describe the bug in the panel and hit Debug it.

You'll see the agent's activity live: every tool call as a trace line, its reasoning as cards, and token usage at the bottom. Any code change opens a diff with a modal Apply / Reject — nothing is written without you.

Related MCP server: agnt

MCP server (for Claude Code, Cursor, …)

Run "Broccoli: Start MCP Server" from the command palette (or set broccoli.mcp.autoStart). Then register it with your agent:

# Claude Code
claude mcp add --transport http broccoli http://127.0.0.1:4923/mcp

// Cursor (~/.cursor/mcp.json)
{
  "mcpServers": {
    "broccoli": { "url": "http://127.0.0.1:4923/mcp" }
  }
}

The agent gets 16 tools: session lifecycle (start_debug_session by launch-config name, restart, stop), breakpoints (incl. conditional), stepping (continue_execution, step_over/into/out — each blocks until the next stop and returns the stop reason, top frame and a locals preview), inspection (get_stack_trace, inspect_variables, expand_variable), read_source, get_debugger_state for cheap orientation, and propose_code_fix — which still shows you the modal diff.

Settings:

Safety model

These are properties of the implementation, not the prompt:

• No expression evaluation — the agent cannot run code in the debuggee.

• No silent edits — every change goes through a modal diff; line numbers are validated against the real file first; if the file changed while you reviewed, the apply is auto-rejected.

• Workspace-scoped reads — read_source and propose_code_fix refuse paths outside open workspace folders.

• Validated input — every tool call (internal or MCP) is checked against its JSON Schema before touching the debugger.

• Bounded runs — turn cap, token budget, cancellation, and per-request timeouts.

• Localhost-only MCP — bound to 127.0.0.1, optional bearer auth, DNS-rebinding protection.

Development

npm install
npm run compile     # typecheck + esbuild bundle
npm test            # unit + integration (real js-debug sessions against test-fixtures/)

test-fixtures/ contains small buggy Node programs (off-by-one, wrong accumulator, async race, uncaught throw) used by the integration tests — and handy for trying the agent yourself: open test-fixtures/ as a workspace and ask Broccoli why sum is NaN.

See architecture.md for the full design.