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.
git clone --depth 1 https://github.com/mhmdreza-rafiei/agent-toolsWrote 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/rules/mhmdreza-rafiei/agent-tools/api-design)<a href="https://agentmods.dev/rules/mhmdreza-rafiei/agent-tools/api-design"><img src="https://agentmods.dev/badge/rules/mhmdreza-rafiei/agent-tools/api-design/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/rules/mhmdreza-rafiei/agent-tools/api-design"><img src="https://agentmods.dev/badge/rules/mhmdreza-rafiei/agent-tools/api-design.svg" alt="Reviewed on agentmods" width="80" 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 | $0.00022 | $0.00426 |
| Opus 5.5 | $0.00009 | $0.00170 |
| Sonnet 5.5 | $0.00004 | $0.00085 |
| Haiku 4.5 | $0.00002 | $0.00043 |
Grade A, and why
api-design 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 2mo 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
API design
Applies when designing or changing an API (REST, RPC, GraphQL). Load for new endpoints, version bumps, breaking changes. Not every chat.
Versioning
- Version explicitly and early.
/v1/...in the path, or a header — pick one and be consistent across the API. - A breaking change bumps the major version; it does not silently change a v1 response shape.
- Deprecate, don't delete: mark the old version deprecated, set a sunset date, document the migration.
Pagination
- Paginate every list endpoint. Default page size; max page size enforced.
- Prefer cursor over offset for large / mutable tables (offset skips rows when data shifts).
- Return pagination metadata in a stable shape (
next_cursor,has_more).
Error shape
- One consistent error shape across the API:
code,message, optionaldetails. HTTP status matches the semantics (4xx client, 5xx server). - Errors are machine-readable: a stable
code, not a free-text message. - 404 for "doesn't exist"; 401 for "who are you"; 403 for "you can't"; 409 for "already exists / conflict". Don't overload 400 for everything.
Idempotency
GET,HEAD,OPTIONSare safe.PUT,DELETEare idempotent.POSTthat creates / charges / sends is made idempotent via an idempotency key (Idempotency-Keyheader) — duplicate retries must not double-charge.
Do not
- Change a response shape without a version bump.
- Return a 200 with an error body. Status must match the body.
- Leak internal stack traces or IDs in error responses.
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.
- 2mo ago First seen · 48 lines · 22 tokens per session scan A 3d4c84580e2c
api-design is a cursor rule published in the GitHub repository mhmdreza-rafiei/agent-tools (5 stars, last pushed 18d ago), licensed MIT. It adds 22 tokens to every session and 426 once invoked, about $0.0001 per session on Opus 5.5. 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 2026-08-31.
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