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/viktorbezdek/skillstack/api-designnpx skills add viktorbezdek/skillstack --skill api-designgit clone --depth 1 https://github.com/viktorbezdek/skillstackWhat 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 | $0.00114 | $0.02773 |
| Opus 5 | $0.00057 | $0.01386 |
| Sonnet 5 | $0.00023 | $0.00555 |
| Haiku 4.5 | $0.00011 | $0.00277 |
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 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 — 338 lines — stays where its author put it; the contents beside it link to each section on GitHub.
API Design
Comprehensive API design skill combining REST, GraphQL, gRPC, and Python library architecture expertise with patterns, templates, and tools for production-grade APIs.
When to Activate
- Creating new API endpoints (REST, GraphQL, gRPC)
- Designing resource hierarchies and schemas
- Writing OpenAPI/Swagger specifications
- Implementing authentication and authorization
- Setting up pagination, filtering, and sorting
- Configuring rate limiting and CORS
- Designing Python library APIs
- Reviewing API designs in pull requests
Decision Tree: API Style Selection
What are you building?
+-- CRUD resources with clear entity model? --> REST
| Best for: resource-oriented operations, caching, wide tooling support
+-- Complex queries with varying client needs? --> GraphQL
| Best for: over-fetching prevention, nested data, multiple client types
+-- High-throughput service-to-service? --> gRPC
| Best for: low latency, strong typing, streaming, polyglot microservices
+-- Reusable Python package? --> Python Library API
Best for: SDKs, internal tooling, developer experience
Quick Reference
RESTful Resource Design
URL Patterns:
/api/v1/users(plural nouns, lowercase with hyphens)/api/v1/organizations/{org_id}/teams(hierarchical, max 2 levels)- Never use verbs:
/getUsersor underscores:/user_profiles
HTTP Methods:
GET- Retrieve (safe, idempotent, cacheable)POST- Create (returns 201 with Location header)PUT- Replace entire resource (idempotent)PATCH- Partial update (only changed fields)DELETE- Remove (idempotent, returns 204)
HTTP Status Codes
| Category | Code | When |
|---|---|---|
| Success | 200 | GET, PUT, PATCH success |
| Success | 201 | POST success (include Location header) |
| Success | 204 | DELETE success |
| Client Error | 400 | Malformed request |
| Client Error | 401 | Missing/invalid authentication |
| Client Error | 403 | Insufficient permissions |
| Client Error | 404 | Resource doesn't exist |
| Client Error | 409 | Duplicate resource |
| Client Error | 422 | Validation errors |
| Client Error | 429 | Rate limit exceeded |
| Server Error | 500 | Unhandled exception |
| Server Error | 503 | Database/service down |
What ships with it
48 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.
- assets/CONTRIBUTING.md.template 6.8 KB
- assets/example-config.py 13 KB runs code
- assets/example-exceptions.py 7.1 KB runs code
- assets/project-structure.txt 6.6 KB
- assets/pyproject.toml.template 3.0 KB
- assets/README.md.template 3.9 KB
- assets/test-structure.txt 8.1 KB
- checklists/api-design-checklist.md 3.8 KB
- checklists/security-review.md 2.3 KB
- evals/evals.json 1.2 KB
- evals/trigger-evals.json 1.9 KB
- examples/fastapi-crud.md 11 KB
- examples/graphql_schema.graphql 8.4 KB
- examples/INDEX.md 786 B
- examples/openapi_spec.yaml 18 KB
- examples/pagination.md 1.2 KB
- examples/pydantic-schemas.md 4.4 KB
- examples/tanstack-start.md 2.4 KB
- examples/testing.md 807 B
- references/api-security.yaml 3.8 KB
- references/architectural-principles.md 13 KB
- references/authentication.md 11 KB
- references/common-patterns.md 12 KB
- references/cors-rate-limiting.md 677 B
- references/error-handlers.md 782 B
- references/fastapi-setup.md 803 B
- references/federation-guide.md 13 KB
- references/graphql-schema.graphql 1.7 KB
- references/grpc-service.proto 2.2 KB
- references/openapi-spec.yaml 3.4 KB
- references/openapi.md 521 B
- references/pep-standards.md 8.9 KB
- references/performance-optimization.md 12 KB
- references/rate-limiting.yaml 2.6 KB
- references/rest-best-practices.md 15 KB
- references/schema-patterns.md 8.7 KB
- references/versioning-strategies.md 7.7 KB
- scripts/api_helper.py 14 KB runs code
- scripts/federation_scaffolder.py 45 KB runs code
- scripts/resolver_generator.py 36 KB runs code
- scripts/schema_analyzer.py 27 KB runs code
- scripts/validate-api-spec.sh 7.1 KB runs code
- templates/error-handler.py 3.4 KB runs code
- templates/fastapi-crud-endpoint.py 4.3 KB runs code
- templates/pydantic-schemas.py 1.6 KB runs code
- templates/rate-limiter.py 2.5 KB runs code
- templates/repository-pattern.py 3.4 KB runs code
- templates/tanstack-server-function.ts 4.8 KB runs code
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 · 338 lines · 114 tokens per session scan A 8781b113d130
api-design is a skill published in the GitHub repository viktorbezdek/skillstack (11 stars, last pushed 2mo ago), licensed MIT. It adds 114 tokens to every session and 2,773 once invoked, about $0.0006 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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