Systematic Debugging — 4-Phase Root Cause Protocol

What it is

Systematic Debugging is a Claude Code skill that enforces a rigorous 4-phase root cause investigation protocol before any code fix is attempted. Instead of jumping straight to a solution, the skill guides Claude through evidence gathering, pattern analysis, hypothesis testing, and only then a targeted fix.

The skill targets developers who find their AI assistant applying quick patches that mask the real bug. By imposing structure on the debugging process, it produces more durable fixes and helps developers understand the underlying problem rather than just silencing the symptom.

How it saves time or tokens

Ad-hoc debugging with an AI assistant often leads to a cycle of patch-test-fail-repatch that burns through tokens and time. The 4-phase protocol front-loads investigation, which means the first fix attempt is more likely to address the actual root cause. Fewer retry loops means fewer tokens spent on failed attempts. The structured output also serves as documentation for the bug, saving time when similar issues arise later.

How to use

1. Copy the skill file to your project:

git clone https://github.com/ChrisWiles/claude-code-showcase.git
cp -r claude-code-showcase/.claude/skills/systematic-debugging .claude/skills/

1. Alternatively, save the skill content manually to .claude/skills/systematic-debugging.md in your project root.

1. Claude Code auto-loads the skill on the next conversation. When you report a bug, Claude will follow the 4-phase protocol automatically.

Example

The 4-phase protocol in action:

Phase 1 — Investigate
  Read error logs, stack traces, recent git changes
  Reproduce the bug with minimal input

Phase 2 — Analyze Patterns
  Identify which module changed recently
  Check if the failure correlates with specific inputs

Phase 3 — Test Hypotheses
  Hypothesis A: Race condition in async handler
  Test: Add logging before/after lock acquisition
  Result: Confirmed — lock released before callback

Phase 4 — Fix
  Move lock release to after callback completes
  Verify fix against original reproduction steps

Related on TokRepo

• AI Tools for Coding — more AI-powered developer tools and coding assistants
• Prompt Library — curated prompts and skill templates for AI coding workflows

Common pitfalls

• Skipping Phase 1 (investigation) defeats the purpose; resist the urge to jump to Phase 4 even when the fix seems obvious
• The skill works best with reproducible bugs; intermittent failures may require additional logging instrumentation before the protocol can proceed
• Overly broad hypothesis testing in Phase 3 can still consume tokens; keep each hypothesis narrow and testable