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 krzysztofsurdy/code-virtuoso --skill api-designgit clone --depth 1 https://github.com/krzysztofsurdy/code-virtuosoWrote 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/krzysztofsurdy/code-virtuoso/api-design)<a href="https://agentmods.dev/skills/krzysztofsurdy/code-virtuoso/api-design"><img src="https://agentmods.dev/badge/skills/krzysztofsurdy/code-virtuoso/api-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/krzysztofsurdy/code-virtuoso/api-design"><img src="https://agentmods.dev/badge/skills/krzysztofsurdy/code-virtuoso/api-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 | $0.00035 | $0.02788 |
| Opus 5.5 | $0.00014 | $0.01115 |
| Sonnet 5.5 | $0.00007 | $0.00558 |
| Haiku 4.5 | $0.00003 | $0.00279 |
Grade A, and why
api-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 4d 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 — 265 lines — stays where its author put it; the contents beside it link to each section on GitHub.
API Design
Principles and patterns for designing APIs that are consistent, predictable, and easy to evolve. Applies to any language or framework. The focus is protocol-level design decisions, not implementation details.
Treat the API surface as a product: consumers should be able to predict behavior, recover from errors, and integrate without reading source code.
When to use
- Designing a new public or internal API from scratch
- Reviewing an existing API for consistency and usability
- Choosing between REST and GraphQL for a project
- Planning API versioning or migration strategy
- Defining error response contracts across services
- Establishing API standards for a team or organization
REST vs GraphQL
| Aspect | REST | GraphQL |
|---|---|---|
| Best for | CRUD-heavy, resource-oriented domains | Complex, interconnected data with varied client needs |
| Data fetching | Fixed response shapes per endpoint | Client specifies exact fields needed |
| Over-fetching | Common, endpoints return full resources | Eliminated, clients request only what they need |
| Under-fetching | Common, requires multiple round trips | Eliminated, a single query can span relations |
| Caching | Built-in HTTP caching (ETags, Cache-Control) | Requires custom caching (normalized stores, persisted queries) |
| File uploads | Native multipart support | Requires workarounds (multipart spec or separate endpoint) |
| Real-time | Webhooks, SSE, or polling | Subscriptions built into the spec |
| Tooling maturity | Mature: OpenAPI, Postman, HTTP clients | Growing: Apollo, Relay, GraphiQL |
| Learning curve | Lower, builds on existing HTTP knowledge | Higher: schema language, resolvers, query optimization |
| Error handling | HTTP status codes + response body | Executed operations usually return 200 with errors in the response errors array; request errors can use 4xx (GraphQL over HTTP, still a draft) |
| Versioning | URL path, headers, or query params | Schema evolution via deprecation + additive changes |
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.
- 4d ago Changed · +4 lines · -59 tokens per session 0e3a00fa7dcd
- 1mo ago First seen · 261 lines · 94 tokens per session scan A 1fe3d606e39b
api-design is a skill published in the GitHub repository krzysztofsurdy/code-virtuoso (36 stars, last pushed 2d ago), licensed MIT. It adds 35 tokens to every session and 2,788 once invoked, about $0.0001 per session on Opus 5.5. 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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