debug-backend

name	debug-backend
description	Diagnose and fix backend bugs, errors, and exceptions. Use when the user reports a bug, shares an error log/stack trace, or asks to debug an issue.
allowed-tools	Read, Grep, Glob, Bash
metadata	{"tier":"default","cost":"light","side_effects":"none"}

Debug the following backend issue:

$ARGUMENTS

Debugging process

Step 1: Understand the problem

• Parse the error message / stack trace
• Identify the error type and origin file:line

Step 2: Trace the root cause

• Read the source code at the error location
• Trace the call chain upward
• Check related configuration files
• Look for recent changes that might have caused the issue

Step 3: Identify the fix

• Determine the root cause (not just symptoms)
• Consider side effects of the fix
• Check if the same pattern exists elsewhere

Step 4: Apply the fix

• Implement the minimal fix
• Explain WHY it fixes the problem
• Suggest a test case to prevent regression

Common patterns to check

• NullPointerException → missing null checks or uninitialized dependencies
• SQL errors → query syntax, missing columns, type mismatches
• 401/403 → authentication/authorization configuration
• 500 → unhandled exceptions in service layer
• Connection errors → database/service configuration, connection pool exhaustion
• Serialization errors → DTO/entity field mismatches