Dapper — DAP Proxy for Multi-Client Debugging
Dapper is a Debug Adapter Protocol (DAP) proxy that lets multiple clients (VS Code, Claude Code, CLI) share a single debug session. It runs as a proxy between the IDE and the debug adapter, and ships an MCP server so AI agents can drive a live debugger.
For agent-driven debugging, start with dapper help agent. It covers the operating model, the end-to-end debugging loop, and the deeper-dive topics worth consulting on demand.
Pick your task
| You want to... | Run | Then read |
|---|---|---|
| Drive Dapper as an autonomous agent | — | dapper help agent |
| Discover what sessions exist | dapper debug sessions | dapper help sessions |
| Inspect threads / stack / variables | dapper debug threads, … stack-trace, … variables | dapper help debug |
| Set or change breakpoints | dapper debug set-breakpoints … | dapper help breakpoints |
| Step / continue / pause | dapper debug {step,continue,pause} <thread> | dapper help debug |
| Connect an MCP-aware agent | dapper mcp | dapper help mcp |
| Start the proxy yourself (rare) | dapper proxy … | dapper help proxy |
Quick smoke test
# Is anything running? If yes, the table tells you what you can talk to.
dapper debug sessions
If the answer is "No active sessions found.", an IDE or fdb invocation needs to start one first; this CLI only attaches to existing proxies, it does not launch debuggers on its own (use dapper proxy from-config <config.json> for headless workflows — see dapper help proxy).
Help output format
dapper help renders Markdown with terminal styling when stdout is interactive and leaves raw Markdown intact when redirected. Set DAPPER_HELP_FORMAT to auto, plain, or terminal to force the behavior.