agent-dbg Debugger

agent-dbg is a CLI debugger for Node.js wrapping the V8 Inspector (CDP). It uses short @refs for all entities — use them instead of long IDs.

Core Debug Loop

# 1. Launch with breakpoint at first line
agent-dbg launch --brk node app.js

# 2. Set breakpoints at suspicious locations
agent-dbg break src/handler.ts:42
agent-dbg break src/utils.ts:15 --condition "count > 10"

# 3. Run to breakpoint
agent-dbg continue

# 4. Inspect state (shows location, source, locals, stack)
agent-dbg state

# 5. Drill into values
agent-dbg props @v1              # expand object
agent-dbg props @v1 --depth 3    # expand nested 3 levels
agent-dbg eval "items.filter(x => x.active)"

# 6. Fix and verify
agent-dbg set count 0            # change variable
agent-dbg hotpatch src/utils.js  # live-edit (reads file from disk)
agent-dbg continue               # verify fix

Debugging Strategies

Bug investigation — narrow down with breakpoints

agent-dbg launch --brk node app.js
agent-dbg break src/api.ts:50                    # suspect line
agent-dbg break src/api.ts:60 --condition "!user" # conditional
agent-dbg continue
agent-dbg vars                                    # check locals
agent-dbg eval "JSON.stringify(req.body)"         # inspect deeply
agent-dbg step over                               # advance one line
agent-dbg state                                   # see new state

Attach to running/test process

# Start node with inspector
node --inspect app.js
# Or attach by PID
agent-dbg attach 12345
agent-dbg state

Trace execution flow with logpoints (no pause)

agent-dbg logpoint src/auth.ts:20 "login attempt: ${username}"
agent-dbg logpoint src/auth.ts:45 "auth result: ${result}"
agent-dbg continue
agent-dbg console    # see logged output

Exception debugging

agent-dbg catch uncaught          # pause on uncaught exceptions
agent-dbg continue                # runs until exception
agent-dbg state                   # see where it threw
agent-dbg eval "err.message"      # inspect the error
agent-dbg stack                   # full call stack

TypeScript source map support

agent-dbg automatically resolves .ts paths via source maps. Set breakpoints using .ts paths, see .ts source in output. Use --generated to see compiled .js if needed.

Ref System

Every output assigns short refs. Use them everywhere:

• @v1..@vN — variables: agent-dbg props @v1, agent-dbg set @v2 true
• @f0..@fN — stack frames: agent-dbg eval --frame @f1 "this"
• BP#1..N — breakpoints: agent-dbg break-rm BP#1, agent-dbg break-toggle BP#1
• LP#1..N — logpoints: agent-dbg break-rm LP#1

Refs @v/@f reset on each pause. BP#/LP# persist until removed.

Key Flags

• --json — machine-readable JSON output on any command
• --session NAME — target a specific session (default: “default”)
• --generated — bypass source maps, show compiled JS (on state/source/stack)

Command Reference

See references/commands.md for full command details and options.

Tips

• agent-dbg state after stepping always shows location + source + locals — usually enough context
• agent-dbg state -c for source only, -v for vars only, -s for stack only — save tokens
• agent-dbg eval supports await — useful for async inspection
• agent-dbg blackbox "node_modules/**" — skip stepping into dependencies
• agent-dbg hotpatch file reads the file from disk — edit the file first, then hotpatch
• Execution commands (continue, step, pause, run-to) auto-return status
• agent-dbg stop kills the debugged process and daemon