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/kouroshez/coding-os/api-designnpx skills add kouroshez/coding-os --skill api-designgit clone --depth 1 https://github.com/kouroshez/coding-osWhat 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 | $0.00084 | $0.02928 |
| Opus 5 | $0.00042 | $0.01464 |
| Sonnet 5 | $0.00017 | $0.00586 |
| Haiku 4.5 | $0.00008 | $0.00293 |
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 — 233 lines — stays where its author put it; the contents beside it link to each section on GitHub.
API Design — REST + GraphQL Contracts
A practical guide to designing APIs that consumers can build against without surprises. Stack-agnostic; concrete patterns target this project's stack (Go+Fiber for the business backend, Python+FastAPI for the AI adapter, React Native client).
When to Use This Skill
- Adding the first endpoint to a service — the contract you ship now will outlive three implementations.
- Reviewing an OpenAPI / GraphQL schema PR before merge.
- Adding a v2 version of a live endpoint without breaking v1 clients.
- Debating REST vs GraphQL for a new bounded context.
- Designing pagination, idempotency, rate-limit responses, batch endpoints.
- Mapping domain errors (from a use case in your hexagonal architecture) to HTTP responses.
Skip when: writing internal-only RPCs that have one caller and you control both sides — use whatever's fastest.
The Contract Is the Product
Three rules that override everything else:
- Consumers cannot read your code. They read the contract. If the contract is ambiguous, the consumer guesses wrong, and you find out in production.
- Breaking changes are expensive forever. Every consumer must coordinate. Plan as if you can't break things — because at scale, you can't.
- The use case shape is sacred. The API shape is negotiable. Don't bend domain operations to match HTTP idioms. Translate at the adapter boundary (per hexagonal-architecture).
REST vs GraphQL — Decision
Pick REST when:
- Consumers are heterogeneous (mobile + web + 3rd-party). REST is the universal lingua franca.
- Endpoints map cleanly to resources. CRUD-like dominates.
- You need HTTP-native caching (CDN, proxies, conditional GET).
- You want minimal client tooling (no codegen mandatory).
Pick GraphQL when:
- Single consumer team or tightly-coupled clients (e.g. one mobile app + one web app from same team).
- Heavy over-fetching with REST: clients pull 12 fields and use 2.
- Frequent shape evolution that doesn't justify a v2 endpoint.
- You're willing to invest in DataLoader, persisted queries, query complexity limits.
What ships with it
4 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.
- yesterday First seen · 233 lines · 84 tokens per session scan A 02f66d3da7fb
api-design is a skill published in the GitHub repository kouroshez/coding-os (6 stars, last pushed yesterday), licensed Apache-2.0. It adds 84 tokens to every session and 2,928 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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