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 charlieviettq/awesome-agent-skill --skill api-and-interface-designgit clone --depth 1 https://github.com/charlieviettq/awesome-agent-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/charlieviettq/awesome-agent-skill/api-and-interface-design)<a href="https://agentmods.dev/skills/charlieviettq/awesome-agent-skill/api-and-interface-design"><img src="https://agentmods.dev/badge/skills/charlieviettq/awesome-agent-skill/api-and-interface-design/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/charlieviettq/awesome-agent-skill/api-and-interface-design"><img src="https://agentmods.dev/badge/skills/charlieviettq/awesome-agent-skill/api-and-interface-design.svg" alt="Reviewed on agentmods" width="80" 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 | $0.00040 | $0.00459 |
| Opus 5 | $0.00020 | $0.00230 |
| Sonnet 5 | $0.00008 | $0.00092 |
| Haiku 4.5 | $0.00004 | $0.00046 |
Grade A, and why
api-and-interface-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 9d 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 and Interface Design
Contract-first design for HTTP APIs, GraphQL, CLI surfaces, and library module boundaries. Complements secure-api-design (security) and agent-tool-contracts (LLM tools) with general interface ergonomics and evolution rules.
When to use
- New public or cross-team API
- Breaking-change review
- Designing pagination, filtering, idempotency, or error shapes
When not to use
- Internal refactor with no boundary change
- Security-only audit (use
secure-api-design) - Agent tool schema only (use
agent-tool-contracts)
Design checklist
Contract
- Resource naming consistent (nouns, plural collections)
- Versioning strategy documented (URL prefix, header, or additive-only)
- Request/response schemas with examples for happy path + common errors
- Idempotency keys for mutating operations where retries matter
Errors
- Stable machine-readable codes separate from human messages
- HTTP/status mapping documented; no stack traces in client responses
- Validation errors: field-level detail when safe (no PII leakage)
Pagination and lists
- Cursor-based preferred for large/live datasets; offset only when bounded
- Default and max page size documented
- Sort/filter params explicit; reject unknown params predictably
Compatibility
- Additive changes only in minor versions
- Deprecation headers or sunset dates for removals
- Consumer migration notes in changelog
Observability
- Correlation/request IDs in responses or logs
- Rate-limit headers where applicable
Workflow
- Draft resource model and primary use cases
- Write example requests/responses (including errors)
- Run
doubt-driven-revieworsecure-api-designfor high-risk surfaces - Implement with tests locked to contract examples
Output
- Short design note or OpenAPI/GraphQL schema sketch
- Compatibility and deprecation table if evolving an existing API
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.
- 9d ago First seen · 66 lines · 40 tokens per session scan A abb436116cfa
api-and-interface-design is a skill published in the GitHub repository charlieviettq/awesome-agent-skill (25 stars, last pushed 1mo ago), licensed MIT. It adds 40 tokens to every session and 459 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 2026-09-03.
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