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 skills add jeremylongworth-source/AgentSkills --skill api-contract-designgit clone --depth 1 https://github.com/jeremylongworth-source/AgentSkillsWrote 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/jeremylongworth-source/agentskills/api-contract-design)<a href="https://agentmods.dev/skills/jeremylongworth-source/agentskills/api-contract-design"><img src="https://agentmods.dev/badge/skills/jeremylongworth-source/agentskills/api-contract-design.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 | $0.00056 | $0.00341 |
| Opus 5 | $0.00028 | $0.00170 |
| Sonnet 5 | $0.00011 | $0.00068 |
| Haiku 4.5 | $0.00006 | $0.00034 |
Grade A, and why
api-contract-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 7d 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 Contract Design
Core Workflow
- Identify API consumers, use cases, resource model, auth context, and compatibility constraints.
- Define endpoints or methods with request fields, response fields, status codes, errors, pagination, filtering, sorting, and idempotency.
- Specify validation rules, defaults, field ownership, and backward-compatible evolution rules.
- Separate public contract from implementation detail.
- Include examples and edge cases that clients can test against.
- Flag open decisions and review needs before implementation.
Safety Rules
- Do not invent production behavior, security guarantees, rate limits, or auth scopes not present in source material.
- Do not expose internal-only fields, private identifiers, secrets, or customer data in examples.
- Require review for contracts affecting billing, auth, customer data, public APIs, or backward compatibility.
Deliverable Shape
For API contracts, provide:
- Consumer and use case
- Resource model
- Endpoint or method table
- Request and response schemas
- Error and status-code contract
- Idempotency, pagination, filtering, and versioning notes
- Examples and edge cases
- Open decisions and review gates
References
- Read
references/api-contract-design-checklist.mdwhen designing or reviewing an API contract.
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.
- 7d ago First seen · 47 lines · 56 tokens per session scan A 6b46df5084da
api-contract-design is a skill published in the GitHub repository jeremylongworth-source/AgentSkills (1 stars, last pushed 5d ago), licensed MIT. It adds 56 tokens to every session and 341 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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