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/code-saurabh/openskills/api-designnpx skills add CODE-SAURABH/OpenSkills --skill api-designgit clone --depth 1 https://github.com/CODE-SAURABH/OpenSkillsWhat 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 | $0.00079 | $0.03735 |
| Opus 5 | $0.00039 | $0.01868 |
| Sonnet 5 | $0.00016 | $0.00747 |
| Haiku 4.5 | $0.00008 | $0.00374 |
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 yesterday.
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 — 405 lines — stays where its author put it; the contents beside it link to each section on GitHub.
API Design
Approach every API as a product. The developer calling your API is your user. An API that is hard to understand, inconsistent, or unpredictable is a broken product — even if it technically works.
Design the API before writing a single line of implementation. An API is a contract. Changing it after clients depend on it is expensive. Getting it right upfront is cheap.
API Design Principles
- Spec first, implement second. Write the OpenAPI spec, GraphQL schema, or proto file before any implementation. The spec is the contract. Implementation details are irrelevant to the caller.
- Consistency is the most important quality. Every endpoint in an API should behave according to the same rules: same error format, same naming convention, same pagination pattern, same auth mechanism. Inconsistency forces callers to write special-case code for every endpoint.
- APIs are forever. Every field you add is a field you must support until you version or sunset the API. Every field you remove is a breaking change. Design with permanence in mind.
- Design for the caller, not the data model. Your database schema is an implementation detail. Your API shape should reflect what callers need, not what your ORM produces.
- Explicit over implicit. Undefined behaviour in an API becomes the behaviour callers depend on. Make every behaviour explicit: required vs optional fields, error codes, rate limits, pagination behaviour at the end of a list.
- Developer experience is a first-class requirement. An API that requires a PhD to understand will not be adopted. Good error messages, consistent naming, and accurate documentation are as important as correct behaviour.
Step 0: Ground the API Design
Before designing any endpoint, answer these questions:
- Who is the caller? Internal service, third-party developer, mobile app, browser, CLI? Each has different needs (auth mechanism, response size, error verbosity).
- What resources does the API expose? List the core domain entities the API manages.
- What operations does each resource support? CRUD is not always the right decomposition — sometimes
cancel,approve,publishare better verbs than generic CRUD. - What are the read/write patterns? High-read, low-write? Real-time? Bulk operations? Streaming? This determines the API style.
- What are the latency and payload size constraints? A mobile API on a 3G connection has different constraints than a backend-to-backend integration.
- What versioning strategy is needed from day one? If this API will have external consumers, versioning must be designed in before the first endpoint ships.
What ships with it
1 file 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.
- yesterday First seen · 405 lines · 79 tokens per session scan A 7d404bad4212
api-design is a skill published in the GitHub repository CODE-SAURABH/OpenSkills (2 stars, last pushed 1mo ago), licensed MIT. It adds 79 tokens to every session and 3,735 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 2026-08-31.
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