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/s3-presigned-urls-validationgit 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/s3-presigned-urls-validation)<a href="https://agentmods.dev/rules/goranerhartic/cursor-development-rules/s3-presigned-urls-validation"><img src="https://agentmods.dev/badge/rules/goranerhartic/cursor-development-rules/s3-presigned-urls-validation.svg" alt="Measured on agentmods" 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 | $0.00015 | $0.00330 |
| Opus 5 | $0.00008 | $0.00165 |
| Sonnet 5 | $0.00003 | $0.00066 |
| Haiku 4.5 | $0.00002 | $0.00033 |
Grade A, and why
s3-presigned-urls-validation 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 5d 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.
What it actually says
S3 Presigned URLs - Post-Upload Validation
When
- After client uploads to S3 (e.g. to a quarantine prefix), validate content and size before moving to final location or processing.
- Trigger: S3 event notification invoking Lambda on object create in upload bucket/prefix.
Validation Steps
- HeadObject: Get ContentLength, ContentType (and metadata if stored).
- Actual content: Use
GetObjectand stream or read first chunk; run file-type (or similar) on buffer to detect real MIME; compare to allowlist. - Size: Enforce max size; reject if over.
- On pass: Copy to final bucket/prefix or update metadata; optionally delete from quarantine.
- On fail: Delete from quarantine (or move to rejected); log and optionally notify; do not expose invalid content.
Multipart (Large Files)
- For large uploads use S3 multipart (CreateMultipartUpload, UploadPart, CompleteMultipartUpload); client-side or via presigned URLs per part.
- Validate after CompleteMultipartUpload (same as single-part: head + optional content check); enforce total size limit across parts.
Conventions
- Always validate MIME and size server-side; use correlationId in metadata for tracing; quarantine then promote or reject
Anti-Patterns
- Trusting client Content-Type only; no size limit; no quarantine/reject path
See also: s3-presigned-urls-upload.mdc, security.mdc
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.
- 5d ago First seen · 34 lines · 15 tokens per session scan A 1017b0f00872
s3-presigned-urls-validation is a cursor rule published in the GitHub repository GoranErhartic/cursor-development-rules (19 stars, last pushed 6mo ago), licensed MIT. It adds 15 tokens to every session and 330 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.
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