phase-gated-debugging

GeneralSafeClaude Codex

How to Install

This skill comes from a community source. Check the original listing for install instructions.

General Claude Code install: copy SKILL.md to ~/.claude/skills/

Phase-Gated Debugging

Overview

AI coding agents see an error and immediately edit code. They guess at fixes, get it wrong, and spiral. This skill enforces a strict 5-phase protocol where you CANNOT edit source code until the root cause is identified and confirmed.

Based on claude-debug (full plugin with PreToolUse hook enforcement).

When to Use

Use this skill when:

a bug keeps getting "fixed" without resolving the underlying issue
you need to slow an agent down and force disciplined debugging before code edits
the failure is intermittent, a regression, performance-related, or otherwise hard to isolate
you want an explicit user confirmation checkpoint before any fix is applied

The Protocol

Phase 1: REPRODUCE

Run the failing command/test. Capture the exact error. Run 2-3 times for consistency. - Do NOT read source code - Do NOT hypothesize - Do NOT edit any files

Phase 2: ISOLATE

Read code. Add diagnostic logging marked // DEBUG. Re-run with diagnostics. Binary search to narrow down. - Only // DEBUG marked logging is allowed - Do NOT fix the bug even if you see it

Phase 3: ROOT CAUSE

Analyze WHY at the isolated location. Use "5 Whys" technique. Remove debug logging.

State: "This is my root cause analysis: [explanation]. Do you agree, or should I investigate further?"

WAIT for user confirmation. Do NOT proceed without it.

Phase 4: FIX

Remove all // DEBUG lines. Apply minimal change addressing confirmed root cause. - Only edit files related to root cause - Do NOT refactor unrelated code

Phase 5: VERIFY

Run original failing test — must pass. Run related tests. For intermittent bugs, run 5+ times. If verification fails: root cause was wrong, go back to Phase 2.

Bug-Type Strategies

Type	Technique
Crash/Panic	Stack trace backward — trace the bad value to its source
Wrong Output	Binary search — log midpoint, halve search space each iteration
Intermittent	Compare passing vs failing run logs — find ordering divergence
Regression	`git bisect` — find the offending commit
Performance	Timing at stage boundaries — find the bottleneck

Key Rules

NEVER edit source code in phases 1-3 (except // DEBUG in phase 2)
NEVER proceed past phase 3 without user confirmation
ALWAYS reproduce before investigating
ALWAYS verify after fixing

Limitations

Use this skill only when the task clearly matches the scope described above.
Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.