ringsystematic-debugging

Systematic Debugging

Core principle: NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST.

When to Use

Use for ANY technical issue: test failures, bugs, unexpected behavior, performance problems, build failures, integration issues.

Especially when:

• Under time pressure (emergencies make guessing tempting)
• "Just one quick fix" seems obvious
• Previous fix didn't work
• You don't fully understand the issue

The Four Phases

Complete each phase before proceeding to the next.

Phase 1: Root Cause Investigation

MUST complete ALL before Phase 2 (copy to TodoWrite): □ Error message copied verbatim | □ Reproduction confirmed | □ Recent changes reviewed (git diff) | □ Evidence from ALL components | □ Data flow traced (origin → error)

1. Read Error Messages - Stack traces completely, line numbers, file paths, error codes. Don't skip warnings.
2. Reproduce Consistently - Exact steps to trigger. Intermittent → gather more data.
3. Check Recent Changes - git diff, recent commits, new dependencies, config changes.
4. Multi-Component Systems - Log at each boundary: what enters, what exits, env/config state. Run once, analyze, identify failing layer.
5. Trace Data Flow - Error deep in stack? Use root-cause-tracing skill. Quick: Where does bad value originate? Trace up call stack, fix at source not symptom.

Phase 1 Summary: Error: [exact] | Reproduces: [steps] | Recent changes: [commits] | Component evidence: [each] | Data origin: [source]

Phase 2: Pattern Analysis

1. Find Working Examples - Similar working code in codebase. What works that's similar to what's broken?
2. Compare Against References - Read reference implementation COMPLETELY. Don't skim - understand fully.
3. Identify Differences - List EVERY difference (working vs broken). Don't assume "that can't matter."
4. Understand Dependencies - What components, config, environment needed? What assumptions does it make?

Phase 3: Hypothesis Testing

1. Form Single Hypothesis - "I think X is root cause because Y" - Be specific.
2. Test Minimally - SMALLEST possible change. One variable at a time.
3. Verify and Track - H#1: [what] → [result] | H#2: [what] → [result] | H#3: [what] → [STOP if fails] If 3 hypotheses fail: STOP immediately → "3 hypotheses failed, architecture review required" → Discuss with partner before more attempts.
4. When You Don't Know - Say "I don't understand X." Ask for help. Research more.

Phase 4: Implementation

Fix root cause, not symptom:

1. Create Failing Test - Simplest reproduction. Use ring:test-driven-development skill.
2. Implement Single Fix - Address root cause only. ONE change at a time. No "while I'm here" improvements.
3. Verify Fix - Test passes? No other tests broken? Issue resolved?
4. If Fix Doesn't Work - Count fixes. If < 3: Return to Phase 1. If ≥ 3: STOP → Architecture review required.
5. After Fix Verified - Test passes and issue resolved? Move to post-completion review.
6. If 3+ Fixes Failed - Pattern: each fix reveals new problem elsewhere, requires massive refactoring, creates new symptoms. STOP and discuss: Is architecture sound? Should we refactor vs. fix?

Time Limits

Debugging time boxes:

• 30 min without root cause → Escalate
• 3 failed fixes → Architecture review
• 1 hour total → Stop, document, ask for guidance

Red Flags

STOP and return to Phase 1 if thinking:

• "Quick fix for now, investigate later"
• "Just try changing X and see if it works"
• "Add multiple changes, run tests"
• "Skip the test, I'll manually verify"
• "It's probably X, let me fix that"
• "I don't fully understand but this might work"
• "One more fix attempt" (when already tried 2+)
• "Each fix reveals new problem" (architecture issue)

User signals you're wrong:

• "Is that not happening?" → You assumed without verifying
• "Stop guessing" → You're proposing fixes without understanding
• "We're stuck?" → Your approach isn't working

When you see these: STOP. Return to Phase 1.

Quick Reference

Circuit breakers:

• 3 hypotheses fail → STOP, architecture review
• 3 fixes fail → STOP, question fundamentals
• 30 min no root cause → Escalate

Integration with Other Skills

Required sub-skills:

• root-cause-tracing - When error is deep in call stack (Phase 1, Step 5)
• ring:test-driven-development - For failing test case (Phase 4, Step 1)

Complementary:

• defense-in-depth - Add validation after finding root cause
• verification-before-completion - Verify fix worked before claiming success

Required Patterns

This skill uses these universal patterns:

• State Tracking: See skills/shared-patterns/state-tracking.md
• Failure Recovery: See skills/shared-patterns/failure-recovery.md
• Exit Criteria: See skills/shared-patterns/exit-criteria.md
• TodoWrite: See skills/shared-patterns/todowrite-integration.md

Apply ALL patterns when using this skill.