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 SymbolicLight-AGI/contractual-skill --skill api-design-principlesgit clone --depth 1 https://github.com/SymbolicLight-AGI/contractual-skillWrote 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/symboliclight-agi/contractual-skill/api-design-principles)<a href="https://agentmods.dev/skills/symboliclight-agi/contractual-skill/api-design-principles"><img src="https://agentmods.dev/badge/skills/symboliclight-agi/contractual-skill/api-design-principles.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 | $0.00042 | $0.00734 |
| Opus 5 | $0.00021 | $0.00367 |
| Sonnet 5 | $0.00008 | $0.00147 |
| Haiku 4.5 | $0.00004 | $0.00073 |
Grade A, and why
api-design-principles-contractual 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 8d 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 — 88 lines — stays where its author put it; the contents beside it link to each section on GitHub.
API Design Principles Contract
When To Use
Use this Skill when designing or reviewing API resources, endpoints, request and response schemas, error models, pagination, filtering, versioning, authentication boundaries, and developer-facing API ergonomics.
Goal
Produce an API design recommendation that is consistent, maintainable, explicit about tradeoffs, and grounded in the provided product and technical requirements.
Audience
- Backend engineers and API platform owners.
- Frontend, integration, partner, and developer-experience teams that consume the API.
Inputs
- Domain entities, use cases, current endpoint proposal, consumers, auth model, scale expectations, existing conventions, and compatibility constraints.
- Optional: OpenAPI fragments, examples, error cases, rate limits, versioning policy, and migration requirements.
Context
Use REST, GraphQL, and API design principles as general guidance. The task's supplied requirements override generic preferences. Do not invent unavailable platform conventions or production constraints.
Workflow
- Identify resources, actions, consumers, and lifecycle states.
- Separate public API contract, internal implementation, and migration concerns.
- Evaluate naming, methods, status codes, schema shape, errors, pagination, filtering, idempotency, and versioning.
- Recommend a design or compare alternatives with tradeoffs.
- Include examples only when they can be derived from the task.
- Surface security, compatibility, observability, and operational risks.
- Define verification criteria such as contract tests, schema validation, and consumer review.
Permissions
- May draft endpoint designs, schema examples, review comments, and migration notes.
- May not claim an API was deployed, tested, documented, or approved unless the task supplies that evidence.
- May not change code, publish documentation, rotate credentials, or call real services.
Human Gates
Require human approval for breaking changes, auth or permission changes, public API commitments, data retention changes, customer-visible versioning decisions, and production migration plans.
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.
- 8d ago First seen · 88 lines · 42 tokens per session scan A dcbd69358416
api-design-principles-contractual is a skill published in the GitHub repository SymbolicLight-AGI/contractual-skill (21 stars, last pushed 3mo ago), licensed MIT. It adds 42 tokens to every session and 734 once invoked, about $0.0002 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 2026-08-30.
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