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/fastifyWrote 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/fastify)<a href="https://agentmods.dev/skills/j4flmao/agent-skills/fastify"><img src="https://agentmods.dev/badge/skills/j4flmao/agent-skills/fastify.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 | $0.00068 | $0.03976 |
| Opus 5 | $0.00034 | $0.01988 |
| Sonnet 5 | $0.00014 | $0.00795 |
| Haiku 4.5 | $0.00007 | $0.00398 |
Grade A, and why
nodejs-fastify 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 7d 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 — 526 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Node.js Fastify
Purpose
Build Fastify applications with schema-first validation, plugin encapsulation, request/response serialization, and lifecycle hooks.
Agent Protocol
Trigger
User request includes: fastify, fastify server, fastify plugin, fastify schema, fastify hooks, fastify validation, fastify serializer, TypeBox, @fastify/swagger.
Input Context
- Fastify version (4.x, 5.x)
- Validation approach (JSON Schema, TypeBox, Zod)
- Plugin set (swagger, cors, jwt, rate-limit)
- Database (TypeORM, Prisma, Knex)
Output Artifact
Server setup, plugin registration, schema definitions, hook pipeline, route patterns.
Response Format
Produce artifact directly. No preamble, no postamble, no explanations.
Completion Criteria
- Server created with logger and schema validator
- Plugins registered with encapsulation
- Routes defined with JSON Schema validation
- Hooks attached at correct lifecycle points
- Swagger/OpenAPI documentation configured
Max Response Length
4096 tokens
Architecture Decision Trees
Validation: JSON Schema vs TypeBox vs Zod
| Criterion | JSON Schema | TypeBox | Zod |
|---|---|---|---|
| Type inference | Manual | Static<typeof schema> |
z.infer<typeof schema> |
| Code-first | No | Yes | Yes |
| Composition | $ref |
Type.Union, Type.Intersect |
z.union, z.intersection |
| Performance | Fast native compilation | Fastest (TypeCode compiler) | Good |
| Ecosystem | Standard, swagger compatible | Fastify-native | Widely used |
Decision: Need OpenAPI/Swagger docs → JSON Schema or TypeBox. Want maximum type safety → TypeBox. Already using Zod in codebase → Zod.
Plugin vs Register Scope
| Scope | Encapsulation | Use Case |
|---|---|---|
| Root | Global | cors, rate-limiter, jwt, formbody |
| Plugin-level | Encapsulated within plugin | Feature modules, route groups |
| Child | Nested encapsulation | Sub-plugins within feature |
Decision: Infrastructure cross-cutting → Root. Feature-specific → Plugin. Shared helpers → fastify-plugin (bypass encapsulation).
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.
- 7d ago First seen · 526 lines · 68 tokens per session scan A 608a709be6f9
nodejs-fastify is a skill published in the GitHub repository j4flmao/agent-skills (21 stars, last pushed yesterday), licensed MIT. It adds 68 tokens to every session and 3,976 once invoked, about $0.0003 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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