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/ngocsangyem/meowkit/api-design-principlesnpx skills add ngocsangyem/MeowKit --skill api-design-principlesgit clone --depth 1 https://github.com/ngocsangyem/MeowKitWrote 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/ngocsangyem/meowkit/api-design-principles)<a href="https://agentmods.dev/skills/ngocsangyem/meowkit/api-design-principles"><img src="https://agentmods.dev/badge/skills/ngocsangyem/meowkit/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 | $0.00059 | $0.01845 |
| Opus 5 | $0.00030 | $0.00923 |
| Sonnet 5 | $0.00012 | $0.00369 |
| Haiku 4.5 | $0.00006 | $0.00185 |
Grade A, and why
mk:api-design-principles 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 2d 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 — 152 lines — stays where its author put it; the contents beside it link to each section on GitHub.
API Design Principles
Durable interface contracts. Discover the existing contract before proposing a new one.
Ownership
| Owner | Owns | Does NOT own |
|---|---|---|
mk:api-design-principles |
Interface contract: resource/type/message shape, error and authorization requirements, compatibility and deprecation, consumer discovery | Implementation, persistence, security verdict, release |
mk:backend-development |
End-to-end backend change: discovery, classification, service/handler/integration work | Contract authorship, schema/SQL, security verdict, deploy |
mk:database |
Data invariants, schema, migration and recovery, query/index evidence, ORM boundary | API contract, authorization verdict, infrastructure execution |
mk:devops |
Infrastructure-as-code, containers, CI, runtime config, deployment safety design, rollback, incident diagnosis | Deploy approval and execution, security verdict, code root-cause, schema semantics |
Routing rules — identical in all four skills:
- Contract-only API question →
mk:api-design-principles, even in the middle of a task owned by another skill. "Contract" means what a consumer can observe: field set, error shape, status semantics, pagination, versioning. Extending an endpoint without changing any of those is not a contract change. - End-to-end backend change →
mk:backend-development, which invokes the API skill only when a new, public, or breaking contract is in scope. - A message-based change (event, webhook, RPC) splits: the message contract belongs to
mk:api-design-principles; the producer or consumer implementation belongs tomk:backend-development. - Schema, migration, query, index, or ORM work →
mk:database. No other skill writes a migration or generic SQL. - Infrastructure, containers, delivery, or deployment safety →
mk:devops. - An unscoped performance request is triaged by evidence, never by guess:
mk:backend-developmentlocates where the time actually goes, then hands a query or index question tomk:databaseand a capacity or runtime question tomk:devops. No skill invents the target. - Code root cause →
mk:investigate.mk:devopsowns the operational picture — what changed, where it fails, which signal proves it — and hands the defect over. - An auth-sensitive change: the owning skill states the requirement; the security workflow owns the verdict.
- Any production effect →
mk:shipor a human.
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.
- 2d ago First seen · 152 lines · 59 tokens per session scan A cb8ebbf3b8c6
mk:api-design-principles is a skill published in the GitHub repository ngocsangyem/MeowKit (14 stars, last pushed 1mo ago), licensed MIT. It adds 59 tokens to every session and 1,845 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 2026-09-03.
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