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)
- Read Error Messages - Stack traces completely, line numbers, file paths, error codes. Don't skip warnings.
- Reproduce Consistently - Exact steps to trigger. Intermittent → gather more data.
- Check Recent Changes -
git diff, recent commits, new dependencies, config changes.
- Multi-Component Systems - Log at each boundary: what enters, what exits, env/config state. Run once, analyze, identify failing layer.
- 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
- Find Working Examples - Similar working code in codebase. What works that's similar to what's broken?
- Compare Against References - Read reference implementation COMPLETELY. Don't skim - understand fully.
- Identify Differences - List EVERY difference (working vs broken). Don't assume "that can't matter."
- Understand Dependencies - What components, config, environment needed? What assumptions does it make?
Phase 3: Hypothesis Testing
- Form Single Hypothesis - "I think X is root cause because Y" - Be specific.
- Test Minimally - SMALLEST possible change. One variable at a time.
- 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.
- When You Don't Know - Say "I don't understand X." Ask for help. Research more.
Phase 4: Implementation
Fix root cause, not symptom:
- Create Failing Test - Simplest reproduction. Use ring:test-driven-development skill.
- Implement Single Fix - Address root cause only. ONE change at a time. No "while I'm here" improvements.
- Verify Fix - Test passes? No other tests broken? Issue resolved?
- If Fix Doesn't Work - Count fixes. If < 3: Return to Phase 1. If ≥ 3: STOP → Architecture review required.
- After Fix Verified - Test passes and issue resolved? Move to post-completion review.
- 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
| Phase |
Key Activities |
Success Criteria |
| 1. Root Cause |
Read errors, reproduce, check changes, gather evidence, trace data flow |
Understand WHAT and WHY |
| 2. Pattern |
Find working examples, compare differences, understand dependencies |
Identify what's different |
| 3. Hypothesis |
Form theory, test minimally, verify one at a time |
Confirmed or new hypothesis |
| 4. Implementation |
Create test, fix root cause, verify |
Bug resolved, tests pass |
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
Blocker Criteria
STOP and report if:
| Decision Type |
Blocker Condition |
Required Action |
| Cannot reproduce issue |
Bug is intermittent and no consistent reproduction steps |
STOP and gather more data before proceeding |
| 3 hypotheses failed |
Three consecutive hypotheses tested and all failed |
STOP and escalate for architecture review |
| 3 fixes failed |
Three fix attempts made but issue persists |
STOP and question fundamental assumptions |
| 30 minutes without root cause |
Extended investigation without identifying root cause |
STOP and escalate for help |
| Fix reveals new problem |
Each attempted fix creates different symptoms |
STOP and request architecture review |
Cannot Be Overridden
The following requirements CANNOT be waived:
- MUST complete Phase 1 (Root Cause Investigation) before any code changes
- MUST form evidence-based hypothesis before attempting fixes
- CANNOT skip creating a failing test in Phase 4
- MUST stop and escalate after 3 failed hypotheses or fixes
- CANNOT claim fix is complete without fresh verification
Severity Calibration
| Severity |
Condition |
Required Action |
| CRITICAL |
Production system affected |
MUST prioritize and escalate immediately |
| CRITICAL |
Data corruption or loss risk |
MUST stop other work and focus exclusively |
| HIGH |
User-facing functionality broken |
MUST investigate before other tasks |
| HIGH |
Tests failing on main branch |
MUST resolve before merging new code |
| MEDIUM |
Non-critical feature affected |
Should investigate within current session |
| LOW |
Minor behavior deviation |
Fix in next iteration if time permits |
Anti-Rationalization Table
| Rationalization |
Why It's WRONG |
Required Action |
| "Quick fix for now, investigate later" |
Later never comes. Quick fixes mask root causes. |
MUST complete Phase 1 before any code change |
| "Just try changing X and see" |
Guessing wastes time and introduces new bugs |
MUST form hypothesis with evidence first |
| "I'm confident this is the issue" |
Confidence without evidence is guessing |
MUST verify with reproduction steps |
| "One more fix attempt" (after 2+) |
Pattern indicates architecture issue, not bug |
STOP and escalate for architecture review |
| "Each fix reveals new problem" |
Symptom of deeper structural issue |
STOP: architecture review REQUIRED |
| "I don't fully understand but this might work" |
Partial understanding = partial fix = new bugs |
MUST understand root cause before fixing |
| "Skip the test, I'll manually verify" |
Manual verification is unreliable and non-repeatable |
MUST create failing test (Phase 4, Step 1) |
| "Previous run showed it works" |
Stale evidence is not evidence |
MUST re-verify with fresh execution |
Pressure Resistance
| User Says |
Your Response |
| "Just fix it quickly, we don't have time" |
"MUST follow the phases - skipping investigation causes more delays through repeated fixes" |
| "Try this change, I think it'll work" |
"I'll add that as a hypothesis and test it properly in Phase 3" |
| "We've tried 5 fixes, try one more" |
"CANNOT proceed - 3+ failed fixes requires architecture review before more attempts" |
| "Skip the investigation, the cause is obvious" |
"MUST verify the obvious before acting - obvious causes are often wrong" |
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.
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1---2name: lerianstudio-ring-systematic-debugging3description: Systematic Debugging4---56# Systematic Debugging78**Core principle:** NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST.910## When to Use1112Use for ANY technical issue: test failures, bugs, unexpected behavior, performance problems, build failures, integration issues.1314**Especially when:**15- Under time pressure (emergencies make guessing tempting)16- "Just one quick fix" seems obvious17- Previous fix didn't work18- You don't fully understand the issue1920## The Four Phases2122Complete each phase before proceeding to the next.2324### Phase 1: Root Cause Investigation2526**MUST complete ALL before Phase 2 (copy to TodoWrite):**27□ Error message copied verbatim | □ Reproduction confirmed | □ Recent changes reviewed (`git diff`) | □ Evidence from ALL components | □ Data flow traced (origin → error)28291. **Read Error Messages** - Stack traces completely, line numbers, file paths, error codes. Don't skip warnings.302. **Reproduce Consistently** - Exact steps to trigger. Intermittent → gather more data.313. **Check Recent Changes** - `git diff`, recent commits, new dependencies, config changes.324. **Multi-Component Systems** - Log at each boundary: what enters, what exits, env/config state. Run once, analyze, identify failing layer.335. **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.3435**Phase 1 Summary:** Error: [exact] | Reproduces: [steps] | Recent changes: [commits] | Component evidence: [each] | Data origin: [source]3637### Phase 2: Pattern Analysis38391. **Find Working Examples** - Similar working code in codebase. What works that's similar to what's broken?402. **Compare Against References** - Read reference implementation COMPLETELY. Don't skim - understand fully.413. **Identify Differences** - List EVERY difference (working vs broken). Don't assume "that can't matter."424. **Understand Dependencies** - What components, config, environment needed? What assumptions does it make?4344### Phase 3: Hypothesis Testing45461. **Form Single Hypothesis** - "I think X is root cause because Y" - Be specific.472. **Test Minimally** - SMALLEST possible change. One variable at a time.483. **Verify and Track** - `H#1: [what] → [result] | H#2: [what] → [result] | H#3: [what] → [STOP if fails]`49 **If 3 hypotheses fail:** STOP immediately → "3 hypotheses failed, architecture review required" → Discuss with partner before more attempts.504. **When You Don't Know** - Say "I don't understand X." Ask for help. Research more.5152### Phase 4: Implementation5354**Fix root cause, not symptom:**55561. **Create Failing Test** - Simplest reproduction. **Use ring:test-driven-development skill.**572. **Implement Single Fix** - Address root cause only. ONE change at a time. No "while I'm here" improvements.583. **Verify Fix** - Test passes? No other tests broken? Issue resolved?594. **If Fix Doesn't Work** - Count fixes. If < 3: Return to Phase 1. **If ≥ 3: STOP → Architecture review required.**605. **After Fix Verified** - Test passes and issue resolved? Move to post-completion review.616. **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?6263## Time Limits6465**Debugging time boxes:**66- 30 min without root cause → Escalate67- 3 failed fixes → Architecture review68- 1 hour total → Stop, document, ask for guidance6970## Red Flags7172**STOP and return to Phase 1 if thinking:**73- "Quick fix for now, investigate later"74- "Just try changing X and see if it works"75- "Add multiple changes, run tests"76- "Skip the test, I'll manually verify"77- "It's probably X, let me fix that"78- "I don't fully understand but this might work"79- "One more fix attempt" (when already tried 2+)80- "Each fix reveals new problem" (architecture issue)8182**User signals you're wrong:**83- "Is that not happening?" → You assumed without verifying84- "Stop guessing" → You're proposing fixes without understanding85- "We're stuck?" → Your approach isn't working8687**When you see these: STOP. Return to Phase 1.**8889## Quick Reference9091| Phase | Key Activities | Success Criteria |92|-------|---------------|------------------|93| **1. Root Cause** | Read errors, reproduce, check changes, gather evidence, trace data flow | Understand WHAT and WHY |94| **2. Pattern** | Find working examples, compare differences, understand dependencies | Identify what's different |95| **3. Hypothesis** | Form theory, test minimally, verify one at a time | Confirmed or new hypothesis |96| **4. Implementation** | Create test, fix root cause, verify | Bug resolved, tests pass |9798**Circuit breakers:**99- 3 hypotheses fail → STOP, architecture review100- 3 fixes fail → STOP, question fundamentals101- 30 min no root cause → Escalate102103## Integration with Other Skills104105**Required sub-skills:**106- **root-cause-tracing** - When error is deep in call stack (Phase 1, Step 5)107- **ring:test-driven-development** - For failing test case (Phase 4, Step 1)108109**Complementary:**110- **defense-in-depth** - Add validation after finding root cause111- **verification-before-completion** - Verify fix worked before claiming success112113## Blocker Criteria114115STOP and report if:116117| Decision Type | Blocker Condition | Required Action |118|---|---|---|119| Cannot reproduce issue | Bug is intermittent and no consistent reproduction steps | STOP and gather more data before proceeding |120| 3 hypotheses failed | Three consecutive hypotheses tested and all failed | STOP and escalate for architecture review |121| 3 fixes failed | Three fix attempts made but issue persists | STOP and question fundamental assumptions |122| 30 minutes without root cause | Extended investigation without identifying root cause | STOP and escalate for help |123| Fix reveals new problem | Each attempted fix creates different symptoms | STOP and request architecture review |124125### Cannot Be Overridden126127The following requirements CANNOT be waived:128- MUST complete Phase 1 (Root Cause Investigation) before any code changes129- MUST form evidence-based hypothesis before attempting fixes130- CANNOT skip creating a failing test in Phase 4131- MUST stop and escalate after 3 failed hypotheses or fixes132- CANNOT claim fix is complete without fresh verification133134## Severity Calibration135136| Severity | Condition | Required Action |137|---|---|---|138| CRITICAL | Production system affected | MUST prioritize and escalate immediately |139| CRITICAL | Data corruption or loss risk | MUST stop other work and focus exclusively |140| HIGH | User-facing functionality broken | MUST investigate before other tasks |141| HIGH | Tests failing on main branch | MUST resolve before merging new code |142| MEDIUM | Non-critical feature affected | Should investigate within current session |143| LOW | Minor behavior deviation | Fix in next iteration if time permits |144145## Anti-Rationalization Table146147| Rationalization | Why It's WRONG | Required Action |148|-----------------|----------------|-----------------|149| "Quick fix for now, investigate later" | Later never comes. Quick fixes mask root causes. | **MUST complete Phase 1 before any code change** |150| "Just try changing X and see" | Guessing wastes time and introduces new bugs | **MUST form hypothesis with evidence first** |151| "I'm confident this is the issue" | Confidence without evidence is guessing | **MUST verify with reproduction steps** |152| "One more fix attempt" (after 2+) | Pattern indicates architecture issue, not bug | **STOP and escalate for architecture review** |153| "Each fix reveals new problem" | Symptom of deeper structural issue | **STOP: architecture review REQUIRED** |154| "I don't fully understand but this might work" | Partial understanding = partial fix = new bugs | **MUST understand root cause before fixing** |155| "Skip the test, I'll manually verify" | Manual verification is unreliable and non-repeatable | **MUST create failing test (Phase 4, Step 1)** |156| "Previous run showed it works" | Stale evidence is not evidence | **MUST re-verify with fresh execution** |157158## Pressure Resistance159160| User Says | Your Response |161|-----------|---------------|162| "Just fix it quickly, we don't have time" | "MUST follow the phases - skipping investigation causes more delays through repeated fixes" |163| "Try this change, I think it'll work" | "I'll add that as a hypothesis and test it properly in Phase 3" |164| "We've tried 5 fixes, try one more" | "CANNOT proceed - 3+ failed fixes requires architecture review before more attempts" |165| "Skip the investigation, the cause is obvious" | "MUST verify the obvious before acting - obvious causes are often wrong" |166167## Required Patterns168169This skill uses these universal patterns:170- **State Tracking:** See `skills/shared-patterns/state-tracking.md`171- **Failure Recovery:** See `skills/shared-patterns/failure-recovery.md`172- **Exit Criteria:** See `skills/shared-patterns/exit-criteria.md`173- **TodoWrite:** See `skills/shared-patterns/todowrite-integration.md`174175Apply ALL patterns when using this skill.176177---178> Converted and distributed by [TomeVault](https://tomevault.io/claim/lerianstudio) — claim your Tome and manage your conversions.179<!-- tomevault:4.0:skill_md:2026-04-11 -->
