Handling Errors

When to use this skill

• Implementing error handling in new features.
• Designing error-resilient APIs and distributed systems.
• Improving application reliability through Circuit Breakers or Graceful Degradation.
• Standardizing error messages and custom exception hierarchies.

Workflow

1. Categorization
   • Determine if the error is Recoverable (e.g., Network Timeout) or Unrecoverable (e.g., OOM).
2. Strategy Selection
   • Choose a pattern: Fail Fast, Retry, Circuit Breaker, or Graceful Degradation.
3. Implementation
   • Use language-specific best practices (Custom Exceptions, Result Types, or Explicit Returns).
4. Verification
   • Validate that errors are logged with context and resources are cleaned up.

Universal Patterns

Circuit Breaker

# Logic: CLOSED -> failure threshold reached -> OPEN (wait timeout) -> HALF_OPEN (test)

Error Aggregation

class ErrorCollector {
  private errors: Error[] = [];
  add(error: Error) { this.errors.push(error); }
  throw() { if (this.errors.length) throw new AggregateError(this.errors); }
}

Graceful Degradation

def with_fallback(primary, fallback):
    try: return primary()
    except Exception: return fallback()

Language-Specific Patterns

Python

• Hierarchy: Use

  ApplicationError(Exception)

  as a base.
• Cleanup: Use

  @contextmanager

  or

  try/finally

  .
• Retry: Implement decorators with exponential backoff.

TypeScript/JS

• Results: Use

  type Result<T, E> = { ok: true; value: T } | { ok: false; error: E }

  .
• Async: Handle Promise rejections explicitly; avoid swallowing errors in

  catch

  .

Rust/Go

• Rust: Prefer

  Result<T, E>

  and the

  ?

  operator.
• Go: Check

  if err != nil

  explicitly; use

  fmt.Errorf("...: %w", err)

  for wrapping.

Best Practices

• Fail Fast: Validate early.
• Preserve Context: Log metadata, stack traces, and timestamps.
• Don't Swallow Errors: Log or re-throw; empty catch blocks are forbidden.
• Cleanup: Always close files and connections.

Resources

• retry-patterns.md
• custom-errors.ts