Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add rules/goranerhartic/cursor-development-rules/error-handlinggit clone --depth 1 https://github.com/GoranErhartic/cursor-development-rulesWhat it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00027 | $0.00567 |
| Opus 5 | $0.00014 | $0.00283 |
| Sonnet 5 | $0.00005 | $0.00113 |
| Haiku 4.5 | $0.00003 | $0.00057 |
Grade A, and why
error-handling scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 42 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Lambda Error Handling
Concepts (Result pattern, RFC 7807): see ../../patterns/error-handling.mdc. Below: Lambda-specific classification and responses.
Error Classification
- Transient: Network timeout, 5xx — retry (SQS: do not add to batchItemFailures only if you want retry; by default failed items are retried)
- Validation/Not Found/Business: 4xx — do not retry; return 400/404/409; set
isRetryable: falsein AppError when using Result for SQS - Infrastructure: DB/connection failure — retry
- Unknown: Log, consider as retryable unless proven otherwise
Result Pattern (minimal implementation)
- AppError:
code,message,statusCode?,isRetryable?,details? - Result<T, E>:
{ success: true; data: T } | { success: false; error: E }; helpers:Result.ok(data),Result.fail(error),Result.isOk(r),Result.isFail(r) - Use for domain/validation; throw for programming errors; in SQS handler push failed messageId to batchItemFailures and do not throw for business/validation (treat as non-retryable)
API Gateway Response
- Success: statusCode 2xx, body JSON string
- Error: Use RFC 7807 ProblemDetails (type, title, status, detail, instance, etc.); set statusCode from error; CORS headers on error response
- Middy: Use
httpErrorHandler(or equivalent) to map thrown errors to response; ensure 4xx/5xx and body format consistent
SQS / Batch
- Do not throw to fail entire batch; catch per message, push
itemIdentifier: record.messageIdto batchItemFailures, return{ batchItemFailures } - For non-retryable (e.g. validation): still add to batchItemFailures so Lambda does not retry; optionally send to DLQ via visibility timeout + redrive policy
Conventions
- Classify errors; use Result for expected failures; map to correct HTTP status and body; log with correlationId; include isRetryable for batch
Anti-Patterns
- Throwing in SQS handler to fail batch; returning 200 on error; no correlationId in logs; generic 500 for validation errors
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 2d ago First seen · 42 lines · 27 tokens per session scan A 052a09b38496
error-handling is a cursor rule published in the GitHub repository GoranErhartic/cursor-development-rules (19 stars, last pushed 6mo ago), licensed MIT. It adds 27 tokens to every session and 567 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
Other cursor rules, from other repositories
angular-20
This rule provides comprehensive best practices and coding standards for Angular development, focusing on modern TypeScript, standalone components, signals, and performance optimizations.
dev-standard
Apache Superset development standards and guidelines for Cursor IDE.
typescript
Changes to these high-fan-out internals can affect every message, delta, element, or rerun. Keep work in them minimal, and benchmark changes with representative stress-test apps.
coolify-ai-docs
Master reference to all Coolify AI documentation in .ai/ directory.
python_lib
Tips and guidelines specific to the development of the Streamlit Python library, not applicable to scripts and e2e tests.
specs
This directory contains product and tech specs for Streamlit features.