error-handling-patterns is agent-read markdown (skill) from khaledsaeed18/dotclaude: Design and review error handling in a codebase: which errors are expected results versus bugs, typed error hierarchies or result types, where to catch (boundaries) and where never to, preserving cause chains, mapping errors to HTTP and CLI exit codes, retries with backoff for the transient, timeouts everywhere, and the logging that makes a failure diagnosable; with idioms for TypeScript, Python, Go, and Rust. Use when adding error handling to new code, when a codebase has inconsistent or swallow.
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What the file says
Error handling has one purpose: when something goes wrong, the right party finds out, with enough context to act, and the system stays in a known state. Every pattern below is judged by that.
## First decision: expected outcome or bug?
- **Expected outcomes** (not found, validation failed, permission denied, rate limited, conflict) are part of the function's contract. Represent them in the type: a result type, a discriminated union, a documented typed error. Callers handle them.
- **Bugs and infrastructure failures** (null where impossible, invariant broken, database down, out of memory) are exceptions. They propagate to a boundary that logs them and fails the operation; code in between does not catch them.
Mixing the two (throwing for "not found", or returning null for "database down") produces both noisy logs and silent failures.
## Represent errors with types
- Base error class per domain (`AppError` with `code`, `httpStatus`, `isOperational`), subclasses for categories (`NotFoundError`, `ValidationError`, `ConflictError`, `UpstreamError`). One place maps code to status and to user message.
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GET https://markdownregistry.com/api/v1/artifacts/art_ayyxppy2hd57mpdv
GET https://markdownregistry.com/api/v1/resolve?ref=khaledsaeed18/dotclaude/error-handling-patterns
GET https://markdownregistry.com/api/v1/blob/256dd350c718c5533cf84a225897efab7fa1100fe1646c2580897d4e19e6ecbf
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