Debug

Cursor-style debug agent for OpenCode — inject probes into CLI and browser apps, capture runtime data, analyze and fix bugs automatically.

Why?

Cursor's Debug Mode works by instrumenting code with probes that POST runtime data to a local HTTP server. This plugin gives OpenCode the same capability — plus CLI apps get automatic reproduction via shell access.

Two modes:

• CLI mode — for Node.js/Python/Go scripts, test suites, server apps. Agent runs the command itself, no user action needed.
• Browser mode — for React/Vue/Svelte apps. User reproduces the bug in their real browser (extensions, cookies, sessions intact). Probes POST data to the agent's HTTP server.

Architecture

┌──────────────────────────────────────────────────┐
│                    OpenCode                       │
│                                                  │
│  ┌─────────┐    ┌───────────────────────────┐   │
│  │  debug   │    │    debug agent prompt     │   │
│  │  agent   │◄───│    (two-mode workflow)     │   │
│  └────┬─────┘    └───────────────────────────┘   │
│       │                                          │
│  ┌────▼──────────────────────────────────────┐   │
│  │              6 Tools                      │   │
│  │                                           │   │
│  │  debug-quick-check  ──► Fast triage       │   │
│  │  debug-server       ──► HTTP capture      │   │
│  │  debug-instrument   ──► Inject probes     │   │
│  │  debug-run-and-capture ─► Run + log       │   │
│  │  debug-read-capture ──► Filter output     │   │
│  │  debug-cleanup      ──► Remove probes     │   │
│  └───────────────────────────────────────────┘   │
│       │                                          │
│  ┌────▼──────────┐   ┌──────────────────┐        │
│  │ /tmp/opencode- │   │ http://localhost │        │
│  │ debug/*.log    │   │ :9514/capture    │        │
│  │ (CLI mode)     │   │ (browser mode)   │        │
│  └────────────────┘   └──────────────────┘        │
└──────────────────────────────────────────────────┘

Tools

debug-quick-check

Fast triage — runs a command, captures exit code/stderr, detects common error patterns (TypeError, ImportError, ECONNREFUSED, etc.). Use this first before the full workflow.

debug-server

Start/stop the HTTP capture server for browser mode. Probes in your app POST runtime data here. Endpoints: /capture, /status, /sessions, /session/:id, /shutdown. CORS enabled — works with Vite, Next.js dev mode, any dev server.

debug-instrument

Inject debug probes into source files. Two modes:

CLI mode (mode: "cli") — console.log probes captured via stdout:

/* @debug:loop-var:abc123 */
console.log("[DEBUG:loop-var]", JSON.stringify({i: i}))

Browser mode (mode: "browser") — fetch() probes POST to debug server:

// #region opencode-debug: loop-var
(function(){
  var _j = JSON.stringify({t:Date.now(), p:"loop-var", s:"abc123", d:{"i": i}});
  fetch("http://localhost:9514/capture", {method:"POST", body:_j, headers:{"Content-Type":"application/json"}, keepalive:true}).catch(function(){});
})();
// #endregion opencode-debug: loop-var

Probe Type	What it does
trace	Logs function entry with arguments
log	Logs variable/expression values
timer	Measures execution time (start + end)
watch	Logs expression value at that point

Supports TypeScript, JavaScript, Python, and Go. Creates .debug.bak backups before modifying files.

debug-run-and-capture

Run a shell command and capture all stdout/stderr to a session-scoped log file. Supports timeout, custom cwd, env vars, session reuse.

debug-read-capture

Read and filter captured output. Two formats:

• format: "raw" — for CLI mode stdout capture
• format: "structured" — for browser mode JSON probe data

Supports keyword search, regex, line ranges.

debug-cleanup

Remove all debug probes and stop the server. Handles both /* @debug: */ markers (CLI) and #region blocks (browser). Can restore from .bak, remove logs, stop server, dry-run.

Installation

opencode plugin opencode-debug

That's it. The tools auto-activate when OpenCode sees error messages.

Usage

CLI app debugging (fully automatic)

Just describe the bug:

"Running node server.js crashes with TypeError"

The agent will triage, instrument, reproduce, analyze, fix, and cleanup — no user action needed.

Browser app debugging (user reproduces)

"Clicking submit in src/Form.tsx crashes the app"

The agent will start the debug server, inject fetch() probes, then say:

"Probes injected. Reproduce the bug in your browser."

You use your real browser at localhost:5173 as normal. The probes POST data back. The agent reads it, fixes the bug, cleans up.

Comparison with Cursor Debug Mode

Feature	Cursor	opencode-debug
Code exploration	✅ IDE context	✅ File access
Hypothesis generation	✅ LLM	✅ LLM
Code instrumentation	✅ IDE extension	✅ Comment markers + fetch() probes
Runtime capture (browser)	✅ IDE debug server	✅ HTTP capture server
Runtime capture (CLI)	❌	✅ Shell pipes to log
Auto-reproduce (CLI)	❌ User reproduces	✅ Agent runs commands
Multi-language	✅ VS Code debugger	✅ TS/JS/Python/Go probes
Cleanup	✅ Automatic	✅ Marker + #region removal
Real browser (extensions, cookies)	✅ User's browser	✅ User's browser

Project Structure

opencode-debug/
├── src/
│   ├── index.ts              # Plugin entry point
│   └── tools/
│       ├── quick-check.ts    # Fast triage
│       ├── debug-server.ts   # HTTP capture server
│       ├── instrument.ts     # Probe injection (CLI + browser)
│       ├── run-and-capture.ts # Run + capture
│       ├── read-capture.ts   # Log reader (raw + structured)
│       └── cleanup.ts        # Probe removal + server stop
├── agent/
│   └── debug.md              # Debug agent system prompt
├── skill/
│   └── SKILL.md              # Auto-activation skill
├── package.json
├── tsconfig.json
└── README.md

Verified Test Results

Unit tests: 16/16 passing (npm run test)

Integration tests in OpenCode 1.14.39:

1. ✅ Plugin loading — all 6 tools registered
2. ✅ Agent selection — --agent debug activates debug agent
3. ✅ Quick-check tool — detects TypeError, ImportError patterns
4. ✅ CLI mode workflow — instrument → run-and-capture → read → fix → cleanup
5. ✅ Browser mode workflow — server start → instrument → simulated POST → read structured data → cleanup + stop server
6. ✅ Skill auto-activation — default agent uses debug tools on error messages
7. ✅ Cleanup — removes both /* @debug: */ markers and #region blocks

License

MIT