Skill

debugging-with-undo

Debug programs using Undo time travel debugging. Record flaky tests, intermittent failures, race conditions, or bugs that don't reproduce reliably. Analyze recordings by traveling backwards through execution history. Use when the user mentions debugging, flaky tests, intermittent bugs, race conditions, `.undo` files (Undo recordings), or asks why something happened in an actual run. This can provide similar results as adding logging statements, but without modifying the code or needing to re-run the program multiple times.

Install

npx claudepluginhub undoio/addons --plugin undo

Tool Access

This skill uses the workspace's default tool permissions.

Preview

Undo provides time travel debugging for Linux programs. This Skill guides you to:

SKILL.md

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debugging-with-undo

Debugging with Undo time travel debugger

Undo provides time travel debugging for Linux programs. This Skill guides you to:

Record program execution to capture failures (especially intermittent ones)

Debug recordings by traveling backwards through execution history

When to record (use record MCP tool)

Record program execution when the user:

Has a flaky test or intermittent failure that doesn't reproduce reliably

Mentions race conditions, threading issues, or concurrency bugs

Wants to capture a failure for later analysis

Needs deterministic replay of a bug

Undo captures the exact execution including thread interleavings, making even race conditions reproducible.

When to debug (use debugging MCP tools)

Debug a recording when the user:

Has a .undo recording file to investigate

Asks "why did this happen" or "how did this value get set"

Wants root cause analysis on a captured failure

Needs to understand execution backwards from a crash or assertion

Workflow

If no recording exists: Use record MCP tool to capture the failure

If recording exists: Use debugging MCP tools to analyze it

Work backwards: Start at the end (where the bug manifested), trace backwards

Important

Never access .undo files directly - they are opaque binary recordings

Never invoke udb, live-record, or undo via Bash - use the Undo MCP tools