Guide · Agent skill
How to use the API Designer agent skill: setup and examples
Updated · written with AI from the project's own documentation and checked against our catalogue data
The API Designer skill is a set of written instructions that tells an AI agent how to turn a plain-language description of a system, such as a booking site or online store, into a structured REST API design. It is useful for developers planning a backend, architects drafting conventions for a team review, and students learning how REST APIs are usually organised. After this guide you will know how to install the skill, how to phrase a request so the agent uses it, and what the output contains and does not guarantee.
API Designersickn33/agentic-awesome-skills · MIT Download the skill Quick start
- 1Get the skill. Download the ZIP from this page and unzip it.
- 2Place it correctly. Put the folder in ~/.claude/skills/ for personal use, or in a project's .claude/skills/ folder, or upload it under Settings → Capabilities → Skills in the Claude apps.
- 3Add the supporting files if needed. Obtain references/domains.md and references/testmu_example.md from the upstream LambdaTest repository if you want the steps that use them.
- 4Ask for a design. Describe your system in plain language, for example a booking site or e-commerce store.
- 5Choose the output level. Answer whether you want endpoints only or a detailed design, unless you already specified it.
- 6Review the result. Check resources, auth, error codes and security points with a person who knows the system.
- 7Optionally generate documentation. Answer yes when asked, and the agent will use the API Documentation skill if it is installed, or offer basic documentation otherwise.
What is an agent skill, and what does api-designer make the agent do?
An agent skill is a folder containing a SKILL.md file of instructions that an AI agent can read and follow for a specific kind of task. The api-designer skill is one of these. Its description is: generates complete, production-ready REST API endpoint specifications for any system or domain the user describes.
Once installed, the agent groups endpoints by resource and, for each one, shows the HTTP method, path, auth headers, example request and response bodies, and relevant error codes. It can also suggest security considerations such as authorization, rate limits and idempotency, and it offers to produce API documentation afterwards. The skill contains no scripts of its own; it is written instructions only.
What do you need before you install it?
You need an AI agent that can read SKILL.md files. The skill also refers to two supporting files, references/domains.md and references/testmu_example.md, which are not included in this catalog copy. They must be obtained from the upstream LambdaTest repository. Until they exist, any step that depends on them is unavailable, though the inline guidance still works.
- An AI agent that can read SKILL.md files
- The two supporting files from the upstream LambdaTest repository (references/domains.md and references/testmu_example.md), needed only for the steps that depend on them
How do you install the api-designer skill?
Download the ZIP of the skill from this page and unzip it. For a personal setup, place the skill folder in ~/.claude/skills/. To limit it to one project, place it in that project's .claude/skills/ folder instead.
If you use the Claude apps, you can instead upload the skill under Settings → Capabilities → Skills.
- Personal use: unzip into ~/.claude/skills/
- Single project: unzip into the project's .claude/skills/ folder
- Claude apps: upload under Settings → Capabilities → Skills
How do you trigger the skill with a natural request?
You do not need a special command. The skill is meant to activate when you ask about API design, API endpoints, REST APIs or API URLs. Phrases such as "what endpoints do I need for..." or "design an API for..." are the kind of request it targets.
If your request does not already say which output you want, the agent will ask whether you want only the endpoints or a complete detailed design. If you state the details up front, it skips that question.
- "Design an API for a hotel booking site."
- "What endpoints do I need for an online store with carts and orders?"
- "Design an API for a small library lending system. Endpoints only."
What does the output look like?
The agent first lists all endpoints, then expands each resource group. Each endpoint gets a short description, a headers table, a request body where relevant, a success response with its status code, and a table of error codes. The skill also asks which extra items you want shown, such as headers or status codes, and includes only those.
List endpoints use a paginated envelope with data and pagination fields, and paths are prefixed with /api/v1/ unless you specify otherwise. Treat the result as a proposed design to review, not a finished specification.
- Endpoints listed first, then grouped by resource
- Headers table, request body, success response and error codes per endpoint
- Paginated envelope for list endpoints, under /api/v1/ by default
- Optional offer to generate API documentation afterwards
How should you review the design before using it?
The skill itself says endpoint lists are proposed designs, not proof of production readiness. The agent infers resources from your description, so it may miss or invent details, especially for an existing API that must match a real contract. Check authorization, input limits, rate limits and idempotency with a person who owns the system.
Because the skill has no scripts and uses no network access, it cannot test the design against a real service. Any commands or generated code should be verified before you apply them.
- Compare the resource list with what your system really needs
- Confirm auth choices (Bearer token, API key, public or admin) match your context
- Review security points such as object authorization, size bounds and redaction of sensitive fields
- Do not rely on it to match an existing contract without the real specification
What people use it for
- Drafting the endpoints for a new hotel booking backend before writing code
- Producing a first draft of REST paths and error codes for a team to review
- Planning a marketplace with products, carts, orders and reviews
- Learning how resources, nested paths such as /hotels/{id}/rooms, and pagination are usually structured
- Creating a starting list of endpoints to compare against an existing design
Frequently asked questions
Is the API Designer agent skill free?
The skill is published under the MIT licence, as stated on this page and in its SKILL.md. Check the licence source linked in the file if you plan to redistribute it.
What do I need to use the api-designer skill?
You need an AI agent that can read SKILL.md files. The skill also refers to two supporting files from the upstream LambdaTest repository, and steps that depend on them are unavailable until you obtain them.
Where do I install the api-designer skill?
Unzip the downloaded ZIP into ~/.claude/skills/ for personal use or into a project's .claude/skills/ folder. In the Claude apps you can upload it under Settings → Capabilities → Skills.
Why is the skill missing references/domains.md and references/testmu_example.md?
This catalog copy does not include those two files. They must be obtained from the upstream LambdaTest repository, and the skill says not to fabricate them or substitute unrelated files with the same name.
Does the skill run code or access the internet?
No. The skill runs no scripts and uses no network access; it consists of written instructions only. Commands and generated code still need checking before you apply them.
Can I use it for an existing API?
It is not a good fit when the design must match a real contract. The agent infers resources from your description and may miss or invent details without the actual system specification.
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Our verdict
Use the api-designer skill if you are planning a new backend, want a consistent first draft of REST conventions for a team to review, or are learning how REST APIs are typically structured. Pick something else, or bring in a human architect, if you need production sign-off or must match an existing API contract, since the skill itself states that endpoint lists are proposed designs rather than proof of production readiness.
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