error-analysis

# Error Analysis Skill

Systematically analyze errors and logs to find root causes.

## When to Use

- Debugging production errors
- Analyzing stack traces
- Investigating log patterns
- Performing root cause analysis
- Categorizing error types

## Reference Documents

- [Log Patterns](./references/log-patterns.md) - Common error patterns by type
- [Root Cause Analysis](./references/root-cause-analysis.md) - RCA techniques
- [Error Categorization](./references/error-categorization.md) - Classifying errors
- [Fix Patterns](./references/fix-patterns.md) - Common fixes by error type

## Analysis Workflow

### 1. Gather Information

```markdown
## Error Report

### Error Message
```
TypeError: Cannot read property 'id' of undefined
    at UserService.getUser (src/services/user.ts:45:23)
    at async Router.handle (src/api/routes.ts:67:12)
```

### Context
- **Environment:** Production
- **Time:** 2024-01-15 14:30 UTC
- **Frequency:** 15 occurrences in last hour
- **Affected Users:** ~5% of requests
- **Recent Changes:** Deploy at 14:00 UTC
```

### 2. Categorize Error

```markdown
## Error Classification

**Type:** Runtime Error
**Category:** Null/Undefined Reference
**Severity:** High (user-facing)

### Common Causes
1. Missing data validation
2. Race condition
3. API contract change
4. Data migration issue
```

### 3. Root Cause Analysis

```markdown
## Root Cause Investigation

### Timeline
- 14:00 - Deploy to production
- 14:25 - First error reported
- 14:30 - Error rate increased

### Hypothesis 1: Deploy introduced bug
- Check: git diff between versions
- Result: New code path added

### Hypothesis 2: Data issue
- Check: Query for affected users
- Result: All have specific condition

### Root Cause
Deploy introduced code that assumes `user.profile` exists,
but 5% of users don't have profiles (legacy accounts).
```

### 4. Implement Fix

```markdown
## Fix Implementation

### Short-term (Hotfix)
```typescript
// Add null check
const userId = user?.profile?.id ?? us