Error Handling

Error Handling Patterns

When to use this skill

• Implementing error handling in new features
• Designing error-resilient APIs
• Debugging production issues or improving application reliability
• Creating better error messages
• Implementing resilience patterns (retry, circuit breaker)
• Handling async/concurrent errors

Workflow

1. Analyze Context: Determine the type of error (Recoverable vs Unrecoverable) and the appropriate handling philosophy (Exceptions vs Result Types).
2. Select Pattern: Choose the right pattern (e.g., Retry, Circuit Breaker, Error Aggregation) based on the requirement.
3. Implement: Apply the pattern using language-specific best practices.
4. Verify: Ensure errors are caught, logged, and handled gracefully without crashing the application.

Instructions

1. Philosophies & Categories

• Recoverable: Network issues, input validation. Handle with Result types or specific exceptions.
• Unrecoverable: OOM, bugs. Let it crash or catch at the top level.
• Exceptions: Use for unexpected/exceptional conditions.
• Result Types: Use for expected errors (validation, business logic).

2. Implementation by Language

• Python: Use custom exception hierarchies (ApplicationError), context managers for cleanup, and decorators for retries.
• TS/JS: Use custom Error classes, Result type pattern for explicit handling, and proper async/await try-catch blocks.
• Rust: Use Result and Option types.
• Go: Use explicit error returns and sentinel errors.

3. Universal Resilience Patterns

• Circuit Breaker: For distributed systems to prevent cascading failures.
• Error Aggregation: Collect multiple errors (e.g., validation) before failing.
• Graceful Degradation: Fallback to cache or default values when primary fails.

4. Best Practices

• Fail Fast: Validate early.
• Context: Include metadata in errors.
• Log properly: Don't spam logs for expected failures.
• Clean up: Always release resources (finally, defer).

Resources

• Exception Hierarchy Design
• Error Recovery Strategies
• Async Error Handling