Debugium

A multi-language debugger with a real-time web UI and LLM integration via MCP.

Debug Python, JavaScript, TypeScript, C, C++, Rust, Java, Scala, and WebAssembly programs from your browser — with AI-driven analysis through the Model Context Protocol.

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Features

Web UI

• Real-time web UI — source viewer, breakpoints, variables (recursive expansion), call stack, console, timeline, watch expressions, findings — all updated live via WebSocket
• Multi-tab source viewer — open multiple files, click stack frames to navigate
• Variable search — filter variables by name with recursive expansion
• Changed-variable highlighting — variables that changed since last stop shown in orange
• Thread selector — switch between threads in multi-threaded programs
• Panel collapse & resize — drag to resize, toggle to collapse; Slim / Standard / Full layout presets
• Dark / light mode toggle
• Auto-reconnect — UI reconnects after a dropped WebSocket, with visual status indicator
• Keyboard shortcuts — F5 continue, F10 step over, F11 step in, Shift+F11 step out, Ctrl/Cmd+D dark mode
• Button animations — in-flight spinner and completion flash for debug commands

Debugging

• Multi-language — Python (debugpy), Node.js/TypeScript (js-debug), C/C++/Rust (lldb-dap), Java (java-debug), Scala (Metals), WebAssembly (lldb-dap), or any DAP adapter via dap.json
• Comprehensive DAP coverage — 35+ DAP requests: breakpoints, stepping, goto, memory read/write, disassembly, and more
• Breakpoints — conditional, logpoints, hit-count, function, data (watchpoints), exception, run-to-cursor (continue_until)
• Multi-session — debug multiple programs simultaneously, with child session routing (js-debug)
• Remote debugging — attach to debugpy, JDWP, or Node inspector running on another machine or container

LLM / MCP Integration

• 64 MCP tools — the full debug session exposed to Claude or any LLM
• Capability-gated tools — tools automatically shown/hidden based on adapter capabilities
• Compound tools — get_debug_context (orient in one call), step_until, step_until_change, run_until_exception, explain_exception, get_call_tree, compare_snapshots, find_first_change
• Execution timeline — every stop recorded with changed variables and stack summary
• Watch expressions — evaluated automatically at every breakpoint, manageable by LLM or UI
• Annotations & findings — pin notes to source lines, record conclusions visible in the UI
• Session export/import — save and restore debugging knowledge across sessions

CLI Control

• Full CLI — 13 subcommands to drive sessions from a second terminal without the web UI
• Auto-discovery — port file at ~/.debugium/port, session logs in ~/.debugium/sessions/

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Install

Claude Code Plugin (recommended)

/plugin marketplace add Algiras/debugium
/plugin install debugium@debugium

Then add to your project's .mcp.json (see MCP Tools below).

macOS / Linux binary

curl -fsSL https://raw.githubusercontent.com/Algiras/debugium/main/install.sh | bash

From source

# Prerequisites: Rust stable + wasm-pack
cargo install wasm-pack

# Build UI
wasm-pack build crates/debugium-ui --target web --out-dir pkg
cp crates/debugium-ui/pkg/cm_init.js         crates/debugium-ui/dist/pkg/
cp crates/debugium-ui/pkg/debugium_ui.js      crates/debugium-ui/dist/pkg/
cp crates/debugium-ui/pkg/debugium_ui_bg.wasm crates/debugium-ui/dist/pkg/

# Build & install server
cargo install --path crates/debugium-server

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Usage

Debug a Python file

debugium launch my_script.py --adapter python

Debug a Node.js / TypeScript file

debugium launch app.js --adapter node
debugium launch app.ts --adapter typescript

Debug C / C++ / Rust

# C or C++ (compile with -g for debug info)
cc -g -O0 main.c -o main && debugium launch ./main --adapter lldb
c++ -g -O0 main.cpp -o main && debugium launch ./main --adapter lldb

# Rust
cargo build && debugium launch target/debug/my_binary --adapter lldb

Debug Java / Scala

# Java (requires microsoft/java-debug adapter)
debugium launch MainClass --adapter java

# Scala (connect to a running Metals DAP server)
debugium launch build-target --adapter metals
debugium launch build-target --adapter metals:5005  # custom port

Attach to a running process (remote debugging)

# Python (debugpy listening on port 5678)
debugium attach --port 5678 --adapter python

# Java (JDWP on port 5005)
debugium attach --port 5005 --adapter java

# Node.js (inspector on port 9229)
debugium attach --port 9229 --adapter node

Or via MCP: attach_session(port=5678, adapter="python", breakpoints=["/path/app.py:42"])

Use a custom adapter via dap.json

# Create a dap.json (see dap.json.example) then:
debugium launch my_program --config ./dap.json

# Or place dap.json in cwd / .debugium/ for auto-discovery:
debugium launch my_program   # finds ./dap.json automatically

Set initial breakpoints

debugium launch my_script.py --adapter python \
  --breakpoint /abs/path/my_script.py:42 \
  --breakpoint /abs/path/helpers.py:15

Enable LLM / MCP integration

Add a .mcp.json to your project root (Claude Code picks this up automatically):

{
  "mcpServers": {
    "debugium": {
      "command": "debugium",
      "args": ["mcp"]
    }
  }
}

Then launch the session normally — the MCP server connects to whichever port is active:

debugium launch my_script.py --adapter python --breakpoint /abs/path/my_script.py:42

Claude Code will now have access to all Debugium MCP tools. See CLAUDE.md for the recommended workflow and SKILL.md for the full tool reference.

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CLI Control Commands

Once a session is running (debugium launch …), you can drive it from a second terminal — or from an LLM agent — without touching the web UI.

Port is auto-discovered from ~/.debugium/port; override with --port.

Global flags (all subcommands)

Flag	Default	Description
--port PORT	~/.debugium/port	Server port to connect to
--session ID	default	Session to target
--json	off	Print raw JSON instead of human-readable output

Inspection

debugium sessions                  # list active sessions
debugium threads                   # list threads
debugium stack                     # show call stack
debugium vars                      # show local variables (auto-resolves top frame)
debugium vars --frame-id 2         # show variables for a specific frame
debugium eval "len(fibs)"          # evaluate expression in top frame
debugium eval "x + 1" --frame-id 2
debugium source path/to/file.py    # print full source file
debugium source path/to/file.py --line 43  # windowed ±10 lines with → marker
debugium context                   # full snapshot: paused-at, stack, locals, source, breakpoints
debugium context --compact         # same but truncated (3 frames, 10 vars)

Breakpoints

debugium bp set FILE:LINE [FILE:LINE …]   # set breakpoints (replaces existing in that file)
debugium bp list                          # list all breakpoints
debugium bp clear                         # clear all breakpoints

Execution control

debugium continue                  # resume execution
debugium step over                 # step over (next line)
debugium step in                   # step into a function call
debugium step out                  # step out of current function

UI annotations (visible in the web UI)

debugium annotate FILE:LINE "message" [--color info|warning|error]
debugium finding "message"         [--level  info|warning|error]

Example workflow

# Terminal A — start the session
debugium launch tests/target_python.py --adapter python \
  --breakpoint "$(pwd)/tests/target_python.py:43"

# Terminal B (or LLM agent) — inspect and drive it
debugium sessions
debugium stack
debugium vars
debugium eval "len(fibs)"
debugium bp set tests/target_python.py:49
debugium continue                  # runs to line 49
debugium vars
debugium step over
debugium context --json            # machine-readable snapshot
debugium annotate tests/target_python.py:43 "called here" --color info
debugium finding "fibs has 10 elements" --level info
debugium bp clear

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MCP Tools

When connected via MCP, 64 tools are available. Key ones:

Category	Tools
Orient	get_debug_context ★ (paused location + locals + stack + source in one call)
Breakpoints	set_breakpoint, set_breakpoints, set_logpoint, list_breakpoints, clear_breakpoints, set_function_breakpoints, set_exception_breakpoints, set_data_breakpoint, list_data_breakpoints, clear_data_breakpoints, breakpoint_locations
Execution	continue_execution, step_over, step_in, step_out, pause, goto, disconnect, terminate, restart
Inspection	get_stack_trace, get_scopes, get_variables, evaluate, get_threads, get_source, get_capabilities, loaded_sources, source_by_reference, step_in_targets
Mutation	set_variable, set_expression
Output	get_console_output, wait_for_output (with from_line to avoid stale matches)
Memory	read_memory, write_memory, disassemble (native debugging)
History	get_timeline, get_variable_history, compare_snapshots, find_first_change
Annotations	annotate, get_annotations, add_finding, get_findings
Watches	add_watch, remove_watch, get_watches
Compound	step_until, step_until_change, continue_until, run_until_exception, explain_exception, get_call_tree, restart_frame
Session	get_sessions, list_sessions, launch_session, attach_session, stop_session, export_session, import_session
Control	goto_targets, cancel_request

Note: step_over, step_in, and step_out are blocking — they wait for the adapter to pause before returning. Safe to chain back-to-back without sleeps. continue_execution returns console_line_count for use with wait_for_output. Tools like read_memory, goto, and restart_frame only appear when the adapter supports them.

See SKILL.md for the full reference with input schemas.

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Keyboard Shortcuts

Key	Action
F5	Continue
F10	Step Over
F11	Step Into
Shift+F11	Step Out
Ctrl/⌘+D	Toggle dark/light mode

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Architecture

debugium-server (Rust + Axum)
├── DAP proxy     — spawns / attaches to debug adapters (debugpy, js-debug, lldb-dap, java-debug, Metals, custom)
├── HTTP API      — /state, /sessions, /annotations, /findings, /watches, /timeline
├── WebSocket     — broadcasts DAP events + enriched stop data (changed vars, timeline) to UI
├── MCP stdio     — JSON-RPC 2.0 server exposing 64 tools for LLM integration
├── CLI control   — 13 subcommands to drive sessions from a second terminal
└── ~/.debugium/  — port file, session logs (events.ndjson), debug log

debugium-ui (Leptos + WASM)
├── CodeMirror 6  — source viewer with breakpoint gutters, exec arrow, LLM annotations, multi-tab
├── Reactive panels — Variables, Stack, Breakpoints, Findings, Watch, Timeline, Console (18 components)
└── WebSocket     — receives events, sends DAP commands, auto-reconnects with status indicator

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Supported Languages & Adapters

Language	--adapter flag	Prerequisite	Verified
Python	python / debugpy	pip install debugpy	✅
Node.js	node / js	js-debug (bundled or build from vscode-js-debug)	✅
TypeScript	typescript / ts / tsx	js-debug + tsx or ts-node in PATH	✅
C / C++	lldb / codelldb	lldb-dap (Xcode on macOS; apt install lldb on Linux)	✅
Rust	lldb / rust	lldb-dap + cargo build	✅
Java	java / jvm	microsoft/java-debug adapter JAR	✅
Scala	metals / scala	Running Metals DAP server	⚠️ (requires running Metals)
WebAssembly	wasm	lldb-dap (LLVM ≥16)	⚠️ (requires WASM-aware LLVM)
Any DAP adapter	--config dap.json	See dap.json.example	✅

Remote debugging

Connect to a DAP server running on another machine (or in a container):

{
  "adapterId": "debugpy",
  "request": "attach",
  "host": "192.168.1.100",
  "port": 5678,
  "pathMappings": [{ "localRoot": ".", "remoteRoot": "/app" }]
}

debugium launch app.py --config remote.json

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License

MIT