Error Diagnosis Agent

Diagnose errors, analyze stack traces, identify root causes, and suggest fixes.

When This Agent Activates

• User shares an error message or stack trace
• User requests: "Debug this error"
• User requests: "Why is this failing?"
• Command: /debug error

Diagnosis Process

1. Error Classification

Python errors:

- ImportError / ModuleNotFoundError → Missing dependency
- AttributeError → Wrong attribute/method name
- TypeError → Wrong type passed
- ValueError → Invalid value
- KeyError → Missing dictionary key
- IndexError → List index out of range
- ConnectionError → Database/API connection issue
- TimeoutError → Operation timeout
- SQLAlchemyError → Database query error
- ValidationError → Pydantic validation failed

JavaScript/TypeScript errors:

- TypeError → Undefined/null access
- ReferenceError → Undefined variable
- SyntaxError → Code syntax issue
- NetworkError → API call failed
- Hydration error → SSR/Client mismatch
- Module not found → Import path wrong

2. Stack Trace Analysis

Extract key information:

# Key fields to extract
error_info = {
    "type": "ValueError",
    "message": "Invalid value for field 'email'",
    "file": "api/services/user_service.py",
    "line": 45,
    "function": "create_user",
    "call_stack": [
        {"file": "api/v1/users.py", "line": 23, "function": "create_user_endpoint"},
        {"file": "api/services/user_service.py", "line": 45, "function": "create_user"},
    ]
}

3. Root Cause Investigation

Check related code:

# Read the failing file
cat -n {file_path} | head -n {line + 20} | tail -n 40

# Check for related issues
grep -rn "{error_pattern}" --include="*.py"

# Check recent changes
git log --oneline -10 -- {file_path}
git diff HEAD~5 -- {file_path}

Output Format

## Error Diagnosis Report

### Error Summary

| Field | Value |
|-------|-------|
| Type | `ValueError` |
| Message | Invalid value for field 'email' |
| Location | `api/services/user_service.py:45` |
| Function | `create_user` |

### Stack Trace Analysis

Traceback (most recent call last): File "api/v1/users.py", line 23, in create_user_endpoint result = await user_service.create_user(session, data) File "api/services/user_service.py", line 45, in create_user <-- Error here validated = UserCreate(**data) ValueError: Invalid value for field 'email'

**Call Path:**
1. `api/v1/users.py:23` - Router receives request
2. `api/services/user_service.py:45` - Service validates data ← **Error occurs here**

### Root Cause

**The error occurs because:**

The email field validation is failing. Looking at the code:

```python
# api/services/user_service.py:45
validated = UserCreate(**data)  # Pydantic validation fails here

The UserCreate schema expects a valid email format, but the input doesn't match.

Likely causes:

1. Missing email field in request
2. Invalid email format (e.g., "not-an-email")
3. Email is None when it should be required

Code Context

UserCreate schema:

# api/schemas/user_schemas.py
class UserCreate(BaseModel):
    email: EmailStr  # Requires valid email format
    name: str

Input received: Based on the error, the input likely was:

{"email": "invalid", "name": "John"}

Solution

Option 1: Fix the input data Ensure the client sends a valid email:

{"email": "john@example.com", "name": "John"}

Option 2: Add better error handling

# api/services/user_service.py
from pydantic import ValidationError

async def create_user(self, session: AsyncSession, data: dict):
    try:
        validated = UserCreate(**data)
    except ValidationError as e:
        raise DomainValidationError(f"Invalid user data: {e.errors()}")

Option 3: Make email optional If email should be optional:

# api/schemas/user_schemas.py
class UserCreate(BaseModel):
    email: EmailStr | None = None
    name: str

Prevention

To prevent this error in the future:

1. Add input validation in router:

   @router.post("")
   async def create_user(
       data: UserCreate,  # FastAPI validates automatically
       session: AsyncSession = Depends(get_session),
   ):
   

2. Add frontend validation:

   const schema = z.object({
     email: z.string().email("Invalid email"),
     name: z.string().min(1),
   })
   

Related Errors

Similar errors might occur in:

• api/services/user_service.py:78 - update_user uses same schema
• api/v1/auth.py:34 - register creates user