Lazarus

Self-healing runner for Python. Run your app under it; when the app crashes, Lazarus captures the full incident (traceback, locals, source context), stores it in a per-project SQLite memory, hands it to a headless Claude agent that reads the code — and past related incidents — patches the root cause, and then restarts (or hot-reloads) to verify the fix held.

Zero runtime dependencies (stdlib only). Needs Python ≥ 3.11 and the claude CLI for healing.

Built by AJTheDev — a North London developer. If Lazarus saves you a 2am debugging session, say hi.

Install

pip install lazarus-agent

Or from source:

git clone https://github.com/AlexJamesDean/lazarus
pip install -e lazarus

(Stdlib-only, so it installs into any venv.)

Per project

cd my-new-project
lazarus init            # writes lazarus.toml, creates .lazarus/, gitignores it
lazarus run app.py      # or: lazarus run -m mypackage.server

That's it. The loop:

1. Run — your program runs as a child process with a crash-reporting hook, breadcrumb capture (last output lines + log records), and — for batch jobs — an optional dead-man timer (max_runtime) that catches hangs and deadlocks by dumping every thread's stack.
2. Capture — an unhandled exception writes a structured report: frames, code lines, local variables, breadcrumbs, fingerprint. When the failing call's arguments are serializable, the crash is frozen into a permanent regression test in .lazarus/repro/ (crash-to-test).
3. Remember — the incident lands in .lazarus/lazarus.db. Recurrences of the same fingerprint bump a counter instead of duplicating. Related past incidents are recalled by fuzzy token similarity (not just exact type/file match), and verified fixes from your other projects are pulled from the hive (~/.lazarus/hive.db).
4. Heal — a headless claude -p agent (Read/Edit/Grep/Glob, plus WebSearch for library errors) patches the root cause with the smallest safe change. A per-attempt model ladder (models = ["haiku", "sonnet", "opus"]) starts cheap and escalates. Implicated files are backed up to .lazarus/backups/ first, and the resulting diff is stored with the attempt. With heal_clones = true the agent also greps for the same bug pattern elsewhere and patches the siblings.
5. Gate — before a patch counts, the canary runs: your test_command plus every captured repro test. A patch that breaks the tests is marked failed immediately and the next attempt is escalated.
6. Verify — Lazarus restarts the program. Clean exit, a long healthy run (verify_seconds), or even a different crash => the fix is verified, recorded in the hive, and written up in the patchlog (.lazarus/PATCHLOG.md) — root cause, fix summary, and diff. The same crash => the attempt is marked failed and the next heal is escalated with the failed diff ("this was tried; it didn't work"). After max_attempts failures on one error it gives up and tells you.

Transient-looking exceptions (ConnectionError, TimeoutError, ...) get one free backoff-retry before any healing — no code patches for a flaky network.

Healing without a restart

For long-running services where a restart is unacceptable, guard the hot path:

from lazarus import guard

@guard                      # or @guard(retries=2)
def handle_request(payload):
    ...

When the function raises, Lazarus heals in-process, importlib.reloads the patched module, and retries the call with the same arguments. (Functions defined in __main__ can't be reloaded — the patch still lands on disk, and lazarus run covers those via restart instead.)

Inspecting the memory

lazarus errors        # every incident: status, hit count, location
lazarus show 3        # full traceback + every fix attempt with its diff
lazarus hive          # verified fixes shared across ALL your projects

Config (lazarus.toml)

Safety rails

• Per-error attempt cap — no infinite patch/crash loops.
• Pre-heal backups of implicated files in .lazarus/backups/incidentN-attemptM/.
• Every attempt's diff is stored; lazarus show makes the agent auditable.
• The healer gets no Bash by default and is told never to touch .lazarus/, lazarus.toml, or anything in protected.
• Non-Python deaths (segfault, OOM kill) are reported, never "healed".

Browser bridge (Lazarus Bridge extension)

Instead of (or alongside) the healer's own WebSearch, Lazarus can research through your browser. Load extension/ as an unpacked extension (chrome://extensions → Developer mode → Load unpacked). While lazarus run or lazarus bridge is up, the extension long-polls 127.0.0.1:8377 and:

• researches crashes — searches the web and opens the top results in background tabs (your active tab, and your video, are never touched), extracts each page to markdown with a bundled defuddle build (fallback extractor included), saves it under .lazarus/research/incidentN/, cites it to the healer, then closes its tabs.
• lets you clip pages — the popup's "Clip this page for Lazarus" button saves whatever you're reading into .lazarus/research/clips/, and clipped pages ride along into the next heal prompt. See a relevant GitHub issue? One click and the healer has it.
• gives Lazarus a voice — with personality = "roast", Lazarus checks what you're watching when the crash lands, roasts you for it via chrome.tts ("Do not pause Never Gonna Give You Up on my account. One of us has a stack trace to read."), announces fixes out loud, and sends a desktop notification with the fix summary. The Claude healer is asked for a bespoke ROAST: line; canned lines cover token-free backends. deadpan keeps the spoken status updates and drops the jokes; the popup has a mute toggle.

The bridge binds localhost only. No extension connected simply means research and speech are skipped. examples/fake_browser.py speaks the same protocol for token-free testing and doubles as protocol documentation.

Troubleshooting

• heal failed: ... 401 Invalid authentication credentials — the claude CLI's own login is stale (it authenticates separately from the desktop app). Run claude login once in a terminal.
• Lazarus can itself be launched from inside a Claude Code session: it strips the session-scoped auth environment before spawning the healer, so the nested CLI authenticates like a normal terminal launch.

Try the demo

cd examples
lazarus run buggy.py      # crashes with KeyError, heals itself, reruns clean
lazarus errors