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 skills/daffy0208/ai-dev-standards/api-designernpx skills add daffy0208/ai-dev-standards --skill api-designergit clone --depth 1 https://github.com/daffy0208/ai-dev-standardsWrote 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/daffy0208/ai-dev-standards/api-designer)<a href="https://agentmods.dev/skills/daffy0208/ai-dev-standards/api-designer"><img src="https://agentmods.dev/badge/skills/daffy0208/ai-dev-standards/api-designer.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 | $0.00041 | $0.02991 |
| Opus 5 | $0.00020 | $0.01496 |
| Sonnet 5 | $0.00008 | $0.00598 |
| Haiku 4.5 | $0.00004 | $0.00299 |
Grade A, and why
API Designer 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.
How it starts
The opening of the file, as written. The whole thing — 543 lines — stays where its author put it; the contents beside it link to each section on GitHub.
API Designer
Design robust, scalable, and developer-friendly APIs.
Core Principles
1. Developer Experience First
- Clear, predictable naming conventions
- Comprehensive documentation
- Helpful error messages
- Consistent patterns across endpoints
2. Design for Evolution
- Versioning strategy from day one
- Backward compatibility
- Deprecation process
- Migration guides for breaking changes
3. Security by Default
- Authentication and authorization
- Rate limiting and throttling
- Input validation and sanitization
- HTTPS only, no exceptions
4. Performance Matters
- Efficient queries and indexing
- Caching strategies
- Pagination for large datasets
- Compression (gzip, brotli)
REST API Design
Resource Naming Conventions
✅ Good (Nouns, plural, hierarchical):
GET /users # List all users
GET /users/123 # Get specific user
POST /users # Create user
PUT /users/123 # Replace user
PATCH /users/123 # Update user
DELETE /users/123 # Delete user
GET /users/123/posts # User's posts (nested)
GET /users/123/posts/456 # Specific post
❌ Bad (Verbs, inconsistent, unclear):
GET /getUsers
POST /createUser
GET /user-list
GET /UserData?id=123
HTTP Methods & Semantics
| Method | Purpose | Idempotent | Safe | Request Body | Response Body |
|---|---|---|---|---|---|
| GET | Retrieve data | Yes | Yes | No | Yes |
| POST | Create resource | No | No | Yes | Yes (created) |
| PUT | Replace resource | Yes | No | Yes | Yes (optional) |
| PATCH | Partial update | No | No | Yes | Yes (optional) |
| DELETE | Remove resource | Yes | No | No | No (204) or Yes |
Idempotent: Multiple identical requests have same effect as single request Safe: Request doesn't modify server state
What ships with it
2 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.
- 5d ago First seen · 543 lines · 41 tokens per session scan A 73070dc8a426
API Designer is a skill published in the GitHub repository daffy0208/ai-dev-standards (36 stars, last pushed 8mo ago), licensed MIT. It adds 41 tokens to every session and 2,991 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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