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:
## 🐛 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
| Pattern | Likely Cause | Action |
|---|
NullPointerException | Null reference not handled | Check null checks, data flow |
ConnectionTimeout | Network/service issue | Check service health, timeout config |
OutOfMemoryError | Memory leak or insufficient heap | Analyze heap dump, check for leaks |
DeadlockException | Concurrent resource contention | Review lock ordering, transaction scope |
401 Unauthorized | Token expired/invalid | Check auth flow, token refresh |
429 Too Many Requests | Rate limiting | Check request frequency, add throttling |
CORS error | Cross-origin misconfiguration | Check server CORS headers |
Log Analysis Steps
- Identify the error: Find the first error in the chain (root cause, not symptom)
- Check timestamp: When did it first occur? Is it recurring?
- Check context: What request/operation triggered it?
- Check stack trace: Which module/function? What line?
- Check related logs: What happened before the error?
- Reproduce: Can you trigger the same error consistently?
# 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
| Severity | Definition | Example |
|---|
| 🔴 Critical | System crash, data loss, security breach, no workaround | Payment charged but order not created |
| 🟠 Major | Core feature broken, has workaround | Login fails on Chrome but works on Firefox |
| 🟡 Minor | Non-core feature issue, cosmetic with functional impact | Sort order wrong on list page |
| 🟢 Trivial | Cosmetic only, typo, UI alignment | Button color slightly off |
Triage Decision Matrix
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:
- Describe the visual issue: Element misaligned? Missing? Wrong state?
- Identify affected component: Which UI component/area?
- Check viewport: Is it responsive-related? Note screen size if visible.
- Compare: Expected design vs actual rendering
- 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:
# 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:
| Status | Check | Likely Root Cause |
|---|
| 400 | Request body/params | Validation logic or schema mismatch |
| 401 | Auth header | Token expired, wrong auth scheme |
| 403 | Permissions | RBAC config, resource ownership |
| 404 | URL path | Route not registered, wrong ID |
| 409 | Business logic | Duplicate entry, state conflict |
| 422 | Validation detail | Semantic validation (format, range) |
| 500 | Server logs | Unhandled exception, null ref, DB error |
| 502/503 | Infrastructure | Upstream service down, deployment in progress |
