Backend Bug Detector

Backend Bug Detector

Provides

• Null and undefined handling checks
• Error handling and control-flow review
• Logic flaw detection in services and handlers
• Data access, async, and backend lifecycle bug checks

Use When

• Debugging backend services
• Investigating failing API behavior
• Reviewing backend code for correctness issues
• Looking for logic, validation, or runtime bugs in server-side systems

Instructions

1. Start with the Affected Flow

• Identify the endpoint, worker, service, or job involved in the bug
• Trace the entry point, request path, or execution path before reviewing unrelated files
• Focus first on the smallest code path that can explain the observed behavior

2. Check Null, Undefined, and Missing Data Handling

• Look for unsafe access to nullable values
• Review optional fields, missing request data, empty query results, and absent configuration
• Check whether code handles not-found, empty, or partial-data cases correctly

Examples:

• accessing properties on possibly null database results
• assuming config values always exist
• using request fields without validation

3. Review Error Handling

• Check whether errors are caught, translated, logged, and returned appropriately
• Flag swallowed exceptions, overly generic catches, and missing error propagation
• Review whether failures leak internal details or hide the real cause

Review targets:

• controller and route handlers
• service-layer exceptions
• background jobs and queue consumers
• database and external API error paths

4. Check Business Logic and Control Flow

• Look for incorrect branching, inverted conditions, unreachable paths, and missing guard clauses
• Review authorization, validation, and state-transition logic carefully
• Check whether edge cases produce unintended results

Examples:

• incorrect status transitions
• duplicate processing paths
• incorrect fallback logic

5. Review Async and Concurrency Behavior

• Check for missing await, unhandled promises, and race conditions
• Review retries, timeouts, transaction boundaries, and parallel operations
• Confirm async work handles cancellation, duplicate execution, or partial failure safely when relevant

6. Review Data Access and Persistence

• Check database queries, repository calls, and cache usage for incorrect assumptions
• Look for missing transaction handling, inconsistent writes, stale reads, or improper error recovery
• Confirm not-found and uniqueness cases are handled correctly

7. Review Validation and Input Handling

• Check whether request params, body fields, headers, and job payloads are validated before use
• Look for missing type checks, range checks, and required-field enforcement
• Confirm invalid input does not silently continue into business logic

8. Check Framework and Runtime-Specific Risks

• Review middleware order, dependency injection wiring, and lifecycle hooks when relevant
• Check whether background workers, scheduled jobs, or event consumers handle retries and idempotency safely
• Look for misconfigured environment-dependent logic that only fails in certain deployments

9. Report Findings by Severity

• Group issues as critical, high, medium, or minor
• Include:
  • issue
  • file
  • explanation
  • suggested fix
• Separate confirmed bugs from likely risks or suspicious patterns

Standard workflow:

1. Identify the affected backend flow
2. Trace entry points and dependent services
3. Review null handling, errors, logic, and async behavior
4. Check persistence and validation paths
5. Return a structured bug report

10. Safety Notes

• Do not report a pattern as a bug unless code behavior supports it
• Prefer file-backed findings over style opinions
• Distinguish correctness issues from maintainability concerns
• Call out uncertainty when runtime wiring, environment config, or infrastructure behavior is not fully visible

Output Format

Critical Bugs

• Issue
• File
• Explanation
• Suggested Fix

High Priority Issues

• Issue
• File
• Explanation
• Suggested Fix

Medium Issues

• Issue
• File
• Explanation
• Suggested Fix

Minor Issues or Improvements

• Issue
• Suggestion

Passed Checks

• Meaningful validations that passed