API Designer
Jeffallan/claude-skills
Designs REST and GraphQL APIs from resource modeling to an OpenAPI 3.1 contract, with versioning, pagination and RFC 7807 error handling.
REST and GraphQL API design patterns, OpenAPI/Swagger specifications, versioning strategies, and authentication patterns.
Install API Contract Design
$ npx skills add rsmdt/the-startup --skill api-contract-design -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install rsmdt/the-startup api-contract-design --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/rsmdt/the-startup.git skills-src && mkdir -p .claude/skills && cp -r skills-src/plugins/team/skills/development/api-contract-design .claude/skills/api-contract-design && rm -rf skills-srcUse ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.
Claude Code skills documentation · loads skills from .claude/skills/
Install the "api-contract-design" agent skill from https://github.com/rsmdt/the-startup/tree/main/plugins/team/skills/development/api-contract-design into .claude/skills/api-contract-design/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-contract-design", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/rsmdt/the-startup/tree/main/plugins/team/skills/development/api-contract-designType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add rsmdt/the-startup --skill api-contract-design -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install rsmdt/the-startup api-contract-design --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/rsmdt/the-startup.git skills-src && mkdir -p .agents/skills && cp -r skills-src/plugins/team/skills/development/api-contract-design .agents/skills/api-contract-design && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "api-contract-design" agent skill from https://github.com/rsmdt/the-startup/tree/main/plugins/team/skills/development/api-contract-design into .agents/skills/api-contract-design/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-contract-design", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add rsmdt/the-startup --skill api-contract-design -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install rsmdt/the-startup api-contract-design --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/rsmdt/the-startup.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/plugins/team/skills/development/api-contract-design .cursor/skills/api-contract-design && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "api-contract-design" agent skill from https://github.com/rsmdt/the-startup/tree/main/plugins/team/skills/development/api-contract-design into .cursor/skills/api-contract-design/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-contract-design", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/rsmdt/the-startup.git --path plugins/team/skills/development/api-contract-design--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add rsmdt/the-startup --skill api-contract-design -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install rsmdt/the-startup api-contract-design --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/rsmdt/the-startup.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/plugins/team/skills/development/api-contract-design .gemini/skills/api-contract-design && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "api-contract-design" agent skill from https://github.com/rsmdt/the-startup/tree/main/plugins/team/skills/development/api-contract-design into .gemini/skills/api-contract-design/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-contract-design", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install rsmdt/the-startup api-contract-designInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add rsmdt/the-startup --skill api-contract-design -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/rsmdt/the-startup.git skills-src && mkdir -p .github/skills && cp -r skills-src/plugins/team/skills/development/api-contract-design .github/skills/api-contract-design && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "api-contract-design" agent skill from https://github.com/rsmdt/the-startup/tree/main/plugins/team/skills/development/api-contract-design into .github/skills/api-contract-design/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-contract-design", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add rsmdt/the-startup --skill api-contract-design -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install rsmdt/the-startup api-contract-design --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/rsmdt/the-startup.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/plugins/team/skills/development/api-contract-design .opencode/skills/api-contract-design && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "api-contract-design" agent skill from https://github.com/rsmdt/the-startup/tree/main/plugins/team/skills/development/api-contract-design into .opencode/skills/api-contract-design/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-contract-design", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
api-contract-design- GitHub stars
- 536
- Token cost
- ~1.1k tokens
- SKILL.md length
- 445 words
- Files
- 7
- Skills in repo
- 27
- Repo updated
- First seen
- Licence
- MIT
At a glance
REST and GraphQL API design patterns, OpenAPI/Swagger specifications, versioning strategies, and authentication patterns.
- Works in 5 steps: Analyze Requirements → Select API Style → Design Contract → …
- Reviewing API contracts
- SKILL.md covers Persona, Interface, Constraints and Reference Materials, plus 1 more section
- Needs API_KEY
What it does
API Contract Design is an agent skill from rsmdt/the-startup. REST and GraphQL API design patterns, OpenAPI/Swagger specifications, versioning strategies, and authentication patterns. Use when designing APIs, reviewing API contracts, evaluating API technologies, or implementing API endpoints.
Its SKILL.md is about 1.1k tokens, which your agent loads only when the skill is triggered. The skill folder holds 8 other files (for example `reference/graphql-patterns.md`, `reference/openapi-patterns.md` and `reference/rest-patterns.md`).
It sits in Backend & APIs, covering API design, OpenAPI specifications and GraphQL. It works with OpenAPI and GraphQL. The repository describes itself as: The Agentic Startup - A collection of Claude Code commands, skills, and agents. The licence is MIT.
When your agent uses it
- Reviewing API contracts
- Evaluating API technologies
- Implementing API endpoints
Example prompts
- “/api-contract-design”
Requirements
- A credential in API_KEY
Workflow steps
5 steps, taken from the step headings in SKILL.md.
What it can do on your machine
Read from SKILL.md and the folder at commit 88d447c. It shows what the files ask for, not the result of running them.
Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md.
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names these keys or tokens, usually read from environment variables:
API_KEY
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.
Context cost
API Contract Design loads about 1.1k tokens when it runs. Until then it costs about 63 tokens; SKILL.md has 445 words of instructions outside code blocks.
Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.
Safety
Auto-check passed
The automated check found no risky patterns in SKILL.md.
Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.
SKILL.md
The full file from rsmdt/the-startup at commit 88d447c, republished under its MIT licence (© rsmdt). 445 words, ~1,078 tokens.
Download SKILL.mdSave it as
.claude/skills/api-contract-design/SKILL.md (or your agent's skills folder). This skill also uses 6 other files; get the full folder from GitHub.- name
- api-contract-design
- description
- REST and GraphQL API design patterns, OpenAPI/Swagger specifications, versioning strategies, and authentication patterns. Use when designing APIs, reviewing API contracts, evaluating API technologies, or implementing API endpoints.
Persona
Act as an API design specialist who creates developer-friendly, consistent, and evolvable API contracts. You apply contract-first design principles, ensuring APIs are defined before implementation to enable parallel development and clear communication.
Design Target: $ARGUMENTS
Interface
ApiStyle { type: REST | GRAPHQL | HYBRID versioning: URL_PATH | HEADER | QUERY_PARAM | DUAL auth: API_KEY | OAUTH2 | JWT | NONE }
DesignDecision { area: string // e.g., pagination, error format, naming choice: string // selected approach rationale: string // why this choice fits }
State { target = $ARGUMENTS apiStyle: ApiStyle decisions: DesignDecision[] contract: string }
Constraints
Always:
- Define the API contract before any implementation begins.
- Apply consistent naming conventions across all endpoints (plural nouns, kebab-case).
- Standardize error response format across all endpoints.
- Include rate limit headers and idempotency keys for non-idempotent operations.
- Use HTTPS exclusively.
- Version the API from day one.
- Document all error codes with resolution steps.
- Identify at least the primary consumer (web, mobile, server, third-party).
- Map each use case to specific resource operations.
Never:
- Expose internal implementation details (database IDs, stack traces) in responses.
- Use GET for operations with side effects.
- Mix REST and RPC styles in the same API.
- Break existing consumers without versioning.
- Authenticate via query parameters (except OAuth callbacks).
- Create deeply nested URLs (more than 2 levels).
- Return different structures for success vs error responses.
Reference Materials
- REST Patterns — Resource modeling, HTTP methods, status codes, error format, pagination, filtering
- GraphQL Patterns — Schema design, queries, mutations, N+1 prevention
- Versioning and Auth — Versioning strategies, API keys, OAuth 2.0, JWT
- OpenAPI Patterns — Specification structure, reusable components
Workflow
1. Analyze Requirements
Identify use cases and consumer needs from target context. Model resources and their relationships. Determine operation types (CRUD + custom actions). Assess non-functional requirements (latency, throughput, caching).
Show full SKILL.md (172 more words)Show less
2. Select API Style
match (requirements) { multiple consumers + different data needs => GRAPHQL or HYBRID simple CRUD + broad ecosystem => REST real-time + subscriptions => GRAPHQL public API + maximum compatibility => REST }
Select versioning strategy (default: DUAL — major in URL, minor in header). Select auth pattern based on consumer type.
3. Design Contract
match (apiStyle.type) { REST => Read reference/rest-patterns.md, design resources + endpoints GRAPHQL => Read reference/graphql-patterns.md, design schema + operations HYBRID => Read both reference files, design unified contract }
For each resource/type:
- Define request/response schemas.
- Specify error scenarios.
- Design pagination approach.
- Document query parameters / arguments.
Read reference/versioning-and-auth.md for auth and versioning details. Read reference/openapi-patterns.md when generating OpenAPI spec.
4. Validate Contract
Consistency checklist:
- Naming conventions (plural nouns, kebab-case)
- Response envelope structure
- Error format across all endpoints
- Pagination approach
- Query parameter patterns
- Date/time formatting (ISO 8601)
Evolution check:
- Additive changes only (new fields, endpoints)
- Deprecation with sunset periods
- Version negotiation support
- Backward compatibility
5. Recommend Next Steps
match (contract) { complete spec => Validate with consumers before implementing partial design => Identify remaining decisions review request => List specific improvements with rationale }
© rsmdt, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
SKILL.md and 6 other files in plugins/team/skills/development/api-contract-design of rsmdt/the-startup.
- SKILL.md
- reference/graphql-patterns.md
- reference/openapi-patterns.md
- reference/rest-patterns.md
- reference/versioning-and-auth.md
- templates/graphql-schema-template.md
- templates/rest-api-template.md
Open the folder on GitHubat commit 88d447c
Compare with similar skills
API Contract Design next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| API Contract Design this skillrsmdt/the-startup | 536 | — | ~1.1k | Automated safety check: Pass | MIT | |
| API DesignerJeffallan/claude-skills | 12k | 2 repos | ~2k | Automated safety check: Pass | MIT | |
| API Designeraiskillstore/marketplace | 430 | 1 repos | ~3.6k | Automated safety check: Pass | None | |
| API Architectcuriositech/some_claude_skills | 243 | 1 repos | ~1.4k | Automated safety check: Pass | MIT | |
| API Designaiskillstore/marketplace | 430 | 1 repos | ~1.8k | Automated safety check: Pass | Apache-2.0 | |
| API Designermajiayu000/claude-skill-registry | 666 | 1 repos | ~3.5k | Automated safety check: Pass | MIT |
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Questions about API Contract Design
What does API Contract Design do?
REST and GraphQL API design patterns, OpenAPI/Swagger specifications, versioning strategies, and authentication patterns. API Contract Design is an agent skill from rsmdt/the-startup. REST and GraphQL API design patterns, OpenAPI/Swagger specifications, versioning strategies, and authentication patterns.
When should I use API Contract Design?
API Contract Design fits situations like: reviewing API contracts; evaluating API technologies; implementing API endpoints.
How do I install API Contract Design in Claude Code?
Run `npx skills add rsmdt/the-startup --skill api-contract-design -a claude-code`. Or copy the skill folder (plugins/team/skills/development/api-contract-design in rsmdt/the-startup) into .claude/skills/api-contract-design in your project. Claude Code loads it when a task matches its description.
How do I install API Contract Design in Codex?
Run `npx skills add rsmdt/the-startup --skill api-contract-design -a codex`. Or copy the skill folder (plugins/team/skills/development/api-contract-design in rsmdt/the-startup) into .agents/skills/api-contract-design in your project. Codex loads it when a task matches its description.
Can I use API Contract Design in Cursor, Gemini CLI or GitHub Copilot?
Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add rsmdt/the-startup --skill api-contract-design -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/api-contract-design, .gemini/skills/api-contract-design, .github/skills/api-contract-design and .opencode/skills/api-contract-design in your project.
What does API Contract Design need to run?
Going by SKILL.md and its folder, API Contract Design needs credentials named API_KEY. Our summary lists: A credential in API_KEY.
Does API Contract Design access the network?
SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.
Is API Contract Design safe to install?
Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.
What licence does API Contract Design use?
API Contract Design is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.
How many tokens does API Contract Design use?
About 1.1k tokens (SKILL.md is roughly 4.3k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.
What are the alternatives to API Contract Design?
Skills that share tags, products or a category with API Contract Design: API Designer (Jeffallan/claude-skills, 12k stars), API Designer (aiskillstore/marketplace, 430 stars), API Architect (curiositech/some_claude_skills, 243 stars) and API Design (aiskillstore/marketplace, 430 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains API Contract Design?
rsmdt (a GitHub user) maintains it in rsmdt/the-startup, which has 536 GitHub stars. The repository holds 27 skills in this directory. The repository was last updated on August 3, 2026.
Source: rsmdt/the-startup on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.