Getting it into your agent
It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.
git clone --depth 1 https://github.com/j4flmao/agent-skillsnpx agentmods add skills/j4flmao/agent-skills/expressWrote 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/express)<a href="https://agentmods.dev/skills/j4flmao/agent-skills/express"><img src="https://agentmods.dev/badge/skills/j4flmao/agent-skills/express.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 5.1 | $0.00081 | $0.03788 |
| Opus 5 | $0.00041 | $0.01894 |
| Sonnet 5 | $0.00016 | $0.00758 |
| Haiku 4.5 | $0.00008 | $0.00379 |
Grade A, and why
nodejs-express-skill 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 6d 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 — 520 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Node.js Express
Purpose
Structure Express.js applications with clean middleware pipeline, error handling, route separation, and validation.
Agent Protocol
Trigger
User request includes: express, express.js, middleware, router, next.js error handling, express app, express setup, express routing, express validation.
Input Context
- App scope (REST API, GraphQL BFF, SSR)
- TypeScript or JavaScript
- Database (Prisma, Mongoose, raw)
- Auth strategy (JWT, session, OAuth)
Output Artifact
Project structure, middleware order, route layout, error handler, validation setup.
Response Format
Produce artifact directly. No preamble, no postamble, no explanations. No filler, no hedging, no transitions. Strip articles a/an/the where unambiguous. Compress output — why use many token when few do trick.
Completion Criteria
- Middleware pipeline ordered security -> parsing -> logging -> rate-limit -> routes -> 404 -> error
- Global error handler catches sync + async errors
- All input validated via schema library
- Routes organized by domain module
Max Response Length
4096 tokens
Architecture Decision Trees
Express vs Fastify vs Hono (within Node.js)
| Criterion | Express | Fastify | Hono |
|---|---|---|---|
| Performance | ~30k req/s | ~50k req/s | ~60k req/s |
| Plugin ecosystem | Largest | Growing | Small |
| TypeScript | Manual annotations | Schema-first (TypeBox/Zod) | Full (TypeBox) |
| Serialization | JSON.stringify | Fast JSON serialization | Built-in |
| Middleware model | Callback chain | Plugin registration | Express-like |
| Validation | Manual middleware | Schema-compiled serializer | Middleware-based |
Decision: Largest ecosystem / wide support → Express. Performance + schema-first → Fastify. Edge/Cloudflare Workers → Hono.
Middleware Order Decision
| Layer | Middleware | Position |
|---|---|---|
| Security | Helmet, CORS, CSP | 1st (before any body) |
| Parsing | JSON, URL-encoded | 2nd |
| Observability | Logger, request ID | 3rd |
| Protection | Rate limiter | 4th |
| Auth | JWT/Session check | 5th |
| Routes | Domain routers | 6th |
| Fallback | 404 handler | 7th |
| Error | Global error handler | Last |
What ships with it
4 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.
- 6d ago First seen · 520 lines · 81 tokens per session scan A 5523fda4f709
nodejs-express-skill is a skill published in the GitHub repository j4flmao/agent-skills (21 stars, last pushed yesterday), licensed MIT. It adds 81 tokens to every session and 3,788 once invoked, about $0.0004 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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