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 skills add j4flmao/agent-skills --skill file-storagegit clone --depth 1 https://github.com/j4flmao/agent-skillsWrote 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/skills/j4flmao/agent-skills/file-storage)<a href="https://agentmods.dev/skills/j4flmao/agent-skills/file-storage"><img src="https://agentmods.dev/badge/skills/j4flmao/agent-skills/file-storage/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/skills/j4flmao/agent-skills/file-storage"><img src="https://agentmods.dev/badge/skills/j4flmao/agent-skills/file-storage.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 1 finding, up to high
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- high YARA Match · line 222 YARA rule matched a known malware signature (reverse shell, backdoor, ransomware, C2 framework, or info stealer).Fix: Remove the malware payload or compromised file entirely. Investigate how it entered the skill and audit all other artifacts for additional indicators of compromise.
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 | $0.00091 | $0.05560 |
| Opus 5 | $0.00046 | $0.02780 |
| Sonnet 5 | $0.00018 | $0.01112 |
| Haiku 4.5 | $0.00009 | $0.00556 |
Grade A, and why
backend-file-storage scanned grade A with 2 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 8d 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.
Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
| Client-side validation only | Easily bypassed via curl/Postman | Always validate server-side | Runs shell commandslowCapability
Expected in a hook, worth knowing in a rule or an instructions file.
import { spawn } from 'child_process'; How it starts
The opening of the file, as written. The whole thing — 520 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Backend File Storage
Purpose
Design secure file storage architecture with upload flows, CDN delivery, and processing.
Agent Protocol
Trigger
Exact user phrases: "file upload", "file storage", "S3", "object storage", "Blob storage", "CDN", "signed URL", "file serving", "image upload", "file management", "static assets", "presigned URL", "S3 bucket", "cloud storage", "file processing".
Input Context
Before activating, verify:
- File types accepted and maximum file sizes
- Upload frequency and expected concurrency
- Access patterns (frequently accessed, archival, private)
- CDN requirements (global distribution, cache TTL)
- Processing pipeline (thumbnails, format conversion, virus scan)
Output Artifact
Storage architecture design as formatted text.
Response Format
# Bucket/key design
# Upload flow
# Processing pipeline
// Presigned URL generation
// Security configuration
No preamble. No postamble. No explanations. No filler/hedging/transitions. Compress output — why use many token when few do trick.
Completion Criteria
- Storage provider and bucket architecture selected
- Key naming scheme defined (flat, no sensitive data)
- Upload flow with presigned URLs and server-side validation
- File processing pipeline (virus scan, thumbnail, format conversion)
- Security controls (IAM, encryption, CORS, presigned URL expiry)
- CDN distribution configured with cache strategy and invalidation
Max Response Length
250 lines of configuration and code.
Decision Tree
Storage Provider
What are your requirements?
├── General purpose, CDN origin → S3 (default)
├── Zero egress fees, high bandwidth → Cloudflare R2
├── On-premises / air-gapped → MinIO
├── Microsoft ecosystem → Azure Blob
├── Analytics / ML pipelines → GCS
└── Compliance (HIPAA, PCI, FedRAMP) → verify provider certification
Upload Flow
Who uploads the file?
├── End user (avatar, document, photo)
│ └── Direct-to-storage via presigned URL (no app server in path)
├── Internal tool (admin upload, batch import)
│ └── Presigned URL or direct server upload for small files (<10MB)
├── Server-side generation (report, export)
│ └── Server writes directly to storage, then notifies user
└── Large file (>100MB, video, dataset)
└── Multipart upload / S3 Transfer Acceleration / resumable upload
What ships with it
6 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 8d ago First seen · 520 lines · 91 tokens per session scan A 436c9ae54b2e
backend-file-storage is a skill published in the GitHub repository j4flmao/agent-skills (23 stars, last pushed 5d ago), licensed MIT. It adds 91 tokens to every session and 5,560 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 2 findings (makes network calls, runs shell commands). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.
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