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Error Handling Patterns

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Master error handling patterns across languages including exceptions, Result types, error propagation, and graceful degradation to build resilient applications. Use when implementing error handling, designing APIs, or improving application reliability.

Originally by wshobson · MIT

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Master error handling patterns across languages including exceptions, Result types, error propagation, and graceful degradation to build resilient applications. Use when implementing error handling, designing APIs, or improving application reliability.

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error-handling-patterns/SKILL.md122 lines4.0 KBRawView on GitHub
Frontmatter — 2 properties
nameerror-handling-patterns
descriptionMaster error handling patterns across languages including exceptions, Result types, error propagation, and graceful degradation to build resilient applications. Use when implementing error handling, designing APIs, or improving application reliability.
1---
2name: error-handling-patterns
3description: Master error handling patterns across languages including exceptions, Result types, error propagation, and graceful degradation to build resilient applications. Use when implementing error handling, designing APIs, or improving application reliability.
4---A5 — No allowed-tools declared — no way to tell what this skill may touch
5 
6# Error Handling Patterns
7 
8Build resilient applications with robust error handling strategies that gracefully handle failures and provide excellent debugging experiences.
9 
10## When to Use This Skill
11 
12- Implementing error handling in new features
13- Designing error-resilient APIs
14- Debugging production issues
15- Improving application reliability
16- Creating better error messages for users and developers
17- Implementing retry and circuit breaker patterns
18- Handling async/concurrent errors
19- Building fault-tolerant distributed systems
20 
21## Core Concepts
22 
23### 1. Error Handling Philosophies
24 
25**Exceptions vs Result Types:**
26 
27- **Exceptions**: Traditional try-catch, disrupts control flow
28- **Result Types**: Explicit success/failure, functional approach
29- **Error Codes**: C-style, requires discipline
30- **Option/Maybe Types**: For nullable values
31 
32**When to Use Each:**
33 
34- Exceptions: Unexpected errors, exceptional conditions
35- Result Types: Expected errors, validation failures
36- Panics/Crashes: Unrecoverable errors, programming bugs
37 
38### 2. Error Categories
39 
40**Recoverable Errors:**
41 
42- Network timeouts
43- Missing files
44- Invalid user input
45- API rate limits
46 
47**Unrecoverable Errors:**
48 
49- Out of memory
50- Stack overflow
51- Programming bugs (null pointer, etc.)
52 
53## Detailed patterns and worked examples
54 
55Detailed pattern documentation lives in `references/details.md`. Read that file when the navigation tier above is insufficient.
56 
57## Best Practices
58 
591. **Fail Fast**: Validate input early, fail quickly
602. **Preserve Context**: Include stack traces, metadata, timestamps
613. **Meaningful Messages**: Explain what happened and how to fix it
624. **Log Appropriately**: Error = log, expected failure = don't spam logs
635. **Handle at Right Level**: Catch where you can meaningfully handle
646. **Clean Up Resources**: Use try-finally, context managers, defer
657. **Don't Swallow Errors**: Log or re-throw, don't silently ignore
668. **Type-Safe Errors**: Use typed errors when possible
67 
68```python
69# Good error handling example
70def process_order(order_id: str) -> Order:
71 """Process order with comprehensive error handling."""
72 try:
73 # Validate input
74 if not order_id:
75 raise ValidationError("Order ID is required")
76 
77 # Fetch orderA4 — This skill pulls in web or user content but never says to treat that content as data. A signal, not proof.
78 order = db.get_order(order_id)
79 if not order:
80 raise NotFoundError("Order", order_id)
81 
82 # Process payment
83 try:
84 payment_result = payment_service.charge(order.total)
85 except PaymentServiceError as e:
86 # Log and wrap external service error
87 logger.error(f"Payment failed for order {order_id}: {e}")
88 raise ExternalServiceError(
89 f"Payment processing failed",
90 service="payment_service",
91 details={"order_id": order_id, "amount": order.total}
92 ) from e
93 
94 # Update order
95 order.status = "completed"
96 order.payment_id = payment_result.id
97 db.save(order)
98 
99 return order
100 
101 except ApplicationError:
102 # Re-raise known application errors
103 raise
104 except Exception as e:
105 # Log unexpected errors
106 logger.exception(f"Unexpected error processing order {order_id}")
107 raise ApplicationError(
108 "Order processing failed",
109 code="INTERNAL_ERROR"
110 ) from e
111```
112 
113## Common Pitfalls
114 
115- **Catching Too Broadly**: `except Exception` hides bugs
116- **Empty Catch Blocks**: Silently swallowing errors
117- **Logging and Re-throwing**: Creates duplicate log entries
118- **Not Cleaning Up**: Forgetting to close files, connections
119- **Poor Error Messages**: "Error occurred" is not helpful
120- **Returning Error Codes**: Use exceptions or Result types
121- **Ignoring Async Errors**: Unhandled promise rejections
122 

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