Bug Hunter#

Analyze, reproduce, and report bugs with precision.

When to Use#

✅ USE this skill when:

• Analyzing error logs, stack traces, crash dumps
• Writing structured bug reports
• Triaging and prioritizing bugs
• Root cause analysis from symptoms
• "这个报错是什么原因" / "帮我写个bug单"

❌ DON'T use this skill when:

• Fixing the code → use coding tools
• Writing test cases → use test-case-gen
• Testing APIs → use api-tester

Bug Report Template#

When writing a bug report, use this structure:

markdown

## 🐛 Bug Report

**Title**: [Module] Brief description of the issue

**Severity**: 🔴 Critical / 🟠 Major / 🟡 Minor / 🟢 Trivial
**Priority**: P0-Blocker / P1-High / P2-Medium / P3-Low
**Environment**: OS / Browser / App Version / API Version
**Reporter**: 虫探 🔍
**Date**: YYYY-MM-DD

### Description
Clear, concise description of what went wrong.

### Steps to Reproduce
1. Step one (be specific: URL, button name, exact input)
2. Step two
3. Step three

### Test Data
- Account: xxx
- Input: xxx

### Expected Result
What should happen.

### Actual Result
What actually happened. Include error messages verbatim.

### Evidence
- Screenshot: [attached]
- Log snippet:
\`\`\`
ERROR 2024-01-01 10:00:00 NullPointerException at UserService.java:42
\`\`\`

### Root Cause Analysis (if identified)
- Location: file:line
- Cause: description
- Impact scope: what else might be affected

### Suggested Fix (if obvious)
Brief suggestion for the developer.

Log Analysis#

Common Error Patterns#

PatternLikely CauseActionNullPointerExceptionNull reference not handledCheck null checks, data flowConnectionTimeoutNetwork/service issueCheck service health, timeout configOutOfMemoryErrorMemory leak or insufficient heapAnalyze heap dump, check for leaksDeadlockExceptionConcurrent resource contentionReview lock ordering, transaction scope401 UnauthorizedToken expired/invalidCheck auth flow, token refresh429 Too Many RequestsRate limitingCheck request frequency, add throttlingCORS errorCross-origin misconfigurationCheck server CORS headers

Log Analysis Steps#

1. Identify the error: Find the first error in the chain (root cause, not symptom)
2. Check timestamp: When did it first occur? Is it recurring?
3. Check context: What request/operation triggered it?
4. Check stack trace: Which module/function? What line?
5. Check related logs: What happened before the error?
6. Reproduce: Can you trigger the same error consistently?

bash

# Quick log analysis commands
# Find errors in log file
grep -n -i "error\|exception\|fatal\|failed" app.log | tail -20

# Count error types
grep -oP '\w+Exception' app.log | sort | uniq -c | sort -rn

# Find errors in time range
awk '/2024-01-01 10:0[0-5]/' app.log | grep -i error

# Get context around an error (5 lines before and after)
grep -B5 -A5 "NullPointerException" app.log

Severity Classification#

SeverityDefinitionExample🔴 CriticalSystem crash, data loss, security breach, no workaroundPayment charged but order not created🟠 MajorCore feature broken, has workaroundLogin fails on Chrome but works on Firefox🟡 MinorNon-core feature issue, cosmetic with functional impactSort order wrong on list page🟢 TrivialCosmetic only, typo, UI alignmentButton color slightly off

Triage Decision Matrix#

text

                    High Impact          Low Impact
High Frequency   →  P0 Fix Now          P1 Fix Soon
Low Frequency    →  P1 Fix Soon         P2/P3 Backlog

Root Cause Categories#

When analyzing root cause, classify into:

• Code Defect: Logic error, missing validation, wrong algorithm
• Config Error: Wrong environment config, missing feature flag
• Data Issue: Corrupt data, migration problem, encoding issue
• Infrastructure: Server capacity, network, third-party service
• Design Flaw: Architectural issue, race condition by design
• Requirement Gap: Ambiguous or missing requirement

Tips#

• Always include the exact error message, not a paraphrase
• Screenshots > descriptions for UI bugs
• Include both expected AND actual results — never skip either
• Note if the bug is intermittent (include frequency)
• Check if the bug exists in previous versions (regression?)
• For API bugs, include the full request and response

Screenshot / UI Bug Analysis#

When provided with screenshots:

1. Describe the visual issue: Element misaligned? Missing? Wrong state?
2. Identify affected component: Which UI component/area?
3. Check viewport: Is it responsive-related? Note screen size if visible.
4. Compare: Expected design vs actual rendering
5. Classify: Layout bug / Style bug / Functional state bug / Data display bug

Use the image tool to analyze screenshots, then include findings in the bug report's Evidence section.

API Error Response Analysis#

When analyzing API errors:

bash

# Save full request + response for bug report
curl -v -X POST "https://api.example.com/endpoint" \
  -H "Content-Type: application/json" \
  -d '{"key": "value"}' 2>&1 | tee /tmp/api-debug.log

# Key things to capture:
# - Request URL, method, headers, body
# - Response status code, headers, body
# - Timing information
# - Any redirect chain

Common API error patterns:

StatusCheckLikely Root Cause400Request body/paramsValidation logic or schema mismatch401Auth headerToken expired, wrong auth scheme403PermissionsRBAC config, resource ownership404URL pathRoute not registered, wrong ID409Business logicDuplicate entry, state conflict422Validation detailSemantic validation (format, range)500Server logsUnhandled exception, null ref, DB error502/503InfrastructureUpstream service down, deployment in progress