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/wyattowalsh/agents/api-designernpx skills add wyattowalsh/agents --skill api-designergit clone --depth 1 https://github.com/wyattowalsh/agentsWrote 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/wyattowalsh/agents/api-designer)<a href="https://agentmods.dev/skills/wyattowalsh/agents/api-designer"><img src="https://agentmods.dev/badge/skills/wyattowalsh/agents/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 | $0.00053 | $0.02339 |
| Opus 5 | $0.00026 | $0.01170 |
| Sonnet 5 | $0.00011 | $0.00468 |
| Haiku 4.5 | $0.00005 | $0.00234 |
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 4d 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 — 220 lines — stays where its author put it; the contents beside it link to each section on GitHub.
API Designer
Contract-first API design across REST, GraphQL, and gRPC. Produces OpenAPI 3.1 specs, reviews existing APIs, analyzes backward compatibility, and scaffolds client code.
Canonical Vocabulary
| Term | Definition |
|---|---|
| spec | An OpenAPI 3.1 document (YAML or JSON) describing an API's surface |
| endpoint | A path + method combination in a REST API; a query/mutation in GraphQL; an RPC in gRPC |
| breaking change | Any modification that causes existing clients to fail without code changes |
| non-breaking change | A backward-compatible modification (additive fields, new endpoints, optional params) |
| resource | A domain entity exposed through the API (noun-based URL segment in REST) |
| contract | The formal agreement between API producer and consumer defined by the spec |
| protocol | The API paradigm: REST, GraphQL, or gRPC |
| surface | The complete set of endpoints, types, and operations an API exposes |
| versioning strategy | How breaking changes are communicated: URL path, header, or query parameter |
Dispatch
| $ARGUMENTS | Action |
|---|---|
design <requirements> |
Design a new API from requirements |
spec <code or path> |
Generate OpenAPI 3.1 spec from existing code |
review <spec or path> |
Audit an existing API design |
version <spec or path> |
Versioning and deprecation strategy |
compat <old> <new> |
Backward compatibility diff analysis |
sdk <spec or path> |
Scaffold client code structure |
| Natural language about API design | Auto-detect mode from intent |
| Empty | Show mode menu with examples |
Mode Menu (empty args)
| # | Mode | Example |
|---|---|---|
| 1 | Design | design "User management API with RBAC" |
| 2 | Spec | spec src/routes/ |
| 3 | Review | review openapi.yaml |
| 4 | Version | version openapi.yaml |
| 5 | Compat | compat v1.yaml v2.yaml |
| 6 | SDK | sdk openapi.yaml |
Pick a number or describe what you need.
What ships with it
24 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.
- data/http-conventions.json 1.5 KB
- data/status-codes.json 2.7 KB
- evals/api-design.json 467 B
- evals/compat-mode.json 585 B
- evals/evals.json 2.1 KB
- evals/explicit-invocation.json 928 B
- evals/implicit-trigger.json 799 B
- evals/negative-control.json 453 B
- references/graphql-patterns.md 4.2 KB
- references/grpc-patterns.md 4.8 KB
- references/rest-conventions.md 5.8 KB
- references/versioning-strategies.md 4.6 KB
- scripts/api-endpoint-matrix.py 3.2 KB runs code
- scripts/api-spec-validator.py 10 KB runs code
- scripts/asset_toolkit/__init__.py 303 B runs code
- scripts/asset_toolkit/_shared.py 5.6 KB runs code
- scripts/asset_toolkit/common.py 3.0 KB runs code
- scripts/asset_toolkit/package.py 43 KB runs code
- scripts/asset_toolkit/validate_evals.py 11 KB runs code
- scripts/asset_toolkit/validate_hooks.py 13 KB runs code
- scripts/asset_toolkit/validate_skill.py 3.6 KB runs code
- scripts/check.py 2.2 KB runs code
- scripts/compat-checker.py 8.8 KB runs code
- templates/dashboard.html 8.4 KB
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.
- 4d ago First seen · 220 lines · 53 tokens per session scan A cfb585d533f9
api-designer is a skill published in the GitHub repository wyattowalsh/agents (5 stars, last pushed 2d ago), licensed MIT. It adds 53 tokens to every session and 2,339 once invoked, about $0.0003 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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