systematic-debugging

name	systematic-debugging
description	Use when encountering any bug, test failure, or unexpected behavior, before proposing fixes

Systematic Debugging

Core principle: ALWAYS find root cause before attempting fixes.

NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST

The Four Phases

Phase 1: Root Cause Investigation

BEFORE attempting ANY fix:

1. Read Error Messages Carefully - Stack traces, line numbers, error codes
2. Reproduce Consistently - Exact steps, every time?
3. Check Recent Changes - Git diff, new deps, config changes
4. Gather Evidence in Multi-Component Systems - Log data at each component boundary, run once, analyze WHERE it breaks

Phase 2: Pattern Analysis

1. Find Working Examples - Similar working code in same codebase
2. Compare Against References - Read reference implementation COMPLETELY
3. Identify Differences - List every difference, however small

Phase 3: Hypothesis and Testing

1. Form Single Hypothesis - "I think X is the root cause because Y"
2. Test Minimally - SMALLEST possible change, one variable at a time
3. Verify Before Continuing - Didn't work? Form NEW hypothesis, don't stack fixes

Phase 4: Implementation

1. Create Failing Test Case - MUST have before fixing
2. Implement Single Fix - ONE change at a time, no "while I'm here" improvements
3. Verify Fix - Test passes? No other tests broken?
4. If 3+ Fixes Failed - STOP. Question the architecture, discuss with human partner

Red Flags - STOP and Return to Phase 1

• "Quick fix for now, investigate later"
• "Just try changing X and see if it works"
• "I don't fully understand but this might work"
• Proposing solutions before tracing data flow
• Each fix reveals new problem in different place

Quick Reference

Phase	Key Activity	Success Criteria
1. Root Cause	Read errors, reproduce, check changes	Understand WHAT and WHY
2. Pattern	Find working examples, compare	Identify differences
3. Hypothesis	Form theory, test minimally	Confirmed or new hypothesis
4. Implementation	Create test, fix, verify	Bug resolved, tests pass