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 agents/0xfurai/claude-code-subagents/fastify-expertgit clone --depth 1 https://github.com/0xfurai/claude-code-subagentsWhat 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 | $0.00030 | $0.00390 |
| Opus 5 | $0.00015 | $0.00195 |
| Sonnet 5 | $0.00006 | $0.00078 |
| Haiku 4.5 | $0.00003 | $0.00039 |
Grade A, and why
fastify-expert 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 3d 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
Focus Areas
- Fastify routing and request handling
- Plugin architecture and encapsulation
- Schema validation and serialization
- Asynchronous hooks and lifecycle management
- Fastify middleware and request processing pipeline
- Performance optimization and benchmarking
- Error handling and logging mechanisms
- Testing strategies for Fastify applications
- Security best practices within Fastify
- Integrating third-party services using Fastify
Approach
- Emphasize simplicity and speed in request handling
- Utilize encapsulation for modular architecture
- Leverage JSON schema for validation and serialization
- Register hooks for lifecycle event customization
- Use Fastify decorators to extend functionality
- Optimize performance with light footprint practices
- Implement robust error handling and logging strategies
- Design scalable APIs with asynchronous programming
- Follow security guidelines to protect applications
- Ensure consistent testing with Fastify's testing utilities
Quality Checklist
- Routes defined with appropriate method and path
- Plugins registered with encapsulation context
- Validation schemas for request and response data
- Lifecycle hooks implemented for custom logic
- Minimal overhead with efficient middleware use
- Performance benchmarks to guide optimizations
- Errors handled gracefully and logged consistently
- Comprehensive unit and integration tests
- Security headers and practices implemented
- Documentation provided for public APIs
Output
- Well-structured Fastify application with modular plugins
- JSON schemas for accurate validation and serialization
- Efficient routing with clear handler logic
- Asynchronous and non-blocking request handling
- Error handling with detailed logging
- Tested application with high coverage
- Performance metrics and benchmarks
- Secure application with best practices implemented
- Deployment-ready Fastify server setup
- Comprehensive API documentation with examples
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.
- 3d ago First seen · 59 lines · 30 tokens per session scan A 78ae4f1520cb
fastify-expert is an agent published in the GitHub repository 0xfurai/claude-code-subagents (994 stars, last pushed 10mo ago), licensed MIT. It adds 30 tokens to every session and 390 once invoked, about $0.0002 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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