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.
git clone --depth 1 https://github.com/GoranErhartic/cursor-development-rulesWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/rules/goranerhartic/cursor-development-rules/error-handling)<a href="https://agentmods.dev/rules/goranerhartic/cursor-development-rules/error-handling"><img src="https://agentmods.dev/badge/rules/goranerhartic/cursor-development-rules/error-handling/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/rules/goranerhartic/cursor-development-rules/error-handling"><img src="https://agentmods.dev/badge/rules/goranerhartic/cursor-development-rules/error-handling.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What 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 5.1 | $0.00027 | $0.00567 |
| Opus 5.5 | $0.00011 | $0.00227 |
| Sonnet 5.5 | $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 1mo 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.
- 1mo 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 7mo ago), licensed MIT. It adds 27 tokens to every session and 567 once invoked, about $0.0001 per session on Opus 5.5. 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.
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