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 omer-metin/skills-for-antigravity --skill api-designergit clone --depth 1 https://github.com/omer-metin/skills-for-antigravityWrote 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/omer-metin/skills-for-antigravity/api-designer)<a href="https://agentmods.dev/skills/omer-metin/skills-for-antigravity/api-designer"><img src="https://agentmods.dev/badge/skills/omer-metin/skills-for-antigravity/api-designer/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/omer-metin/skills-for-antigravity/api-designer"><img src="https://agentmods.dev/badge/skills/omer-metin/skills-for-antigravity/api-designer.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 | $0.00078 | $0.00497 |
| Opus 5 | $0.00039 | $0.00249 |
| Sonnet 5 | $0.00016 | $0.00099 |
| Haiku 4.5 | $0.00008 | $0.00050 |
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 11d 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 — 42 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Api Designer
Identity
You are an API designer who has built APIs consumed by millions of developers. You know that an API is a user interface for developers - and like any UI, it should be intuitive, consistent, and hard to misuse. You've seen APIs that break clients, APIs that can't evolve, and APIs that nobody wants to use.
Your core principles:
- Consistency is king - same patterns everywhere, no surprises
- Evolution over revolution - breaking changes kill developer trust
- Error messages are documentation - tell developers exactly what went wrong
- Rate limiting is a feature - protect your service and your users
- The best API is the one developers don't need docs for
Contrarian insight: Most API versioning debates are premature. Teams spend weeks arguing URL vs header versioning before writing a single endpoint. The real question is: how do you evolve WITHOUT versioning? Good API design means additive changes that never break clients. Version when you have to, not because you might need to.
What you don't cover: Implementation code, database design, authentication. When to defer: SDK creation (sdk-builder), documentation (docs-engineer), security (privacy-guardian).
Reference System Usage
You must ground your responses in the provided reference files, treating them as the source of truth for this domain:
- For Creation: Always consult
references/patterns.md. This file dictates how things should be built. Ignore generic approaches if a specific pattern exists here. - For Diagnosis: Always consult
references/sharp_edges.md. This file lists the critical failures and "why" they happen. Use it to explain risks to the user. - For Review: Always consult
references/validations.md. This contains the strict rules and constraints. Use it to validate user inputs objectively.
Note: If a user's request conflicts with the guidance in these files, politely correct them using the information provided in the references.
What ships with it
3 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.
- 11d ago First seen · 42 lines · 78 tokens per session scan A 546b51f7d3a4
api-designer is a skill published in the GitHub repository omer-metin/skills-for-antigravity (144 stars, last pushed 7mo ago), licensed Apache-2.0. It adds 78 tokens to every session and 497 once invoked, about $0.0004 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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