API Contract Lab: Design, Test, and Share API Endpoints in Your Browser

Every API integration starts the same way: somebody sends you a spec, or a URL to some docs, or a Slack message that says "here's the endpoint, it takes these params." Then you spend the next hour piecing together what the API actually does, writing boilerplate fetch calls, manually setting up Postman requests, and generating test data to verify your assumptions. API Contract Lab compresses that entire process into a few seconds.

It's one of three free tools in Wigley Studios Developer Labs, and it solves a specific problem: the gap between receiving an API specification and being ready to build against it. Paste a spec, get everything you need. No signup required.

What API Contract Lab Does

The tool takes an API specification—OpenAPI/Swagger format, a JSON schema, or even raw JSON—and transforms it into something immediately useful. Not a static documentation page, but an interactive workspace where you can explore endpoints, generate mock responses, copy code snippets in your language of choice, and export a complete Postman Collection ready for testing.

Four core capabilities, each solving a distinct friction point in API development:

1. Spec Parsing

Paste an OpenAPI or Swagger spec and get an interactive breakdown of every endpoint in the API. Each route is displayed with its HTTP method, path, parameters (required and optional), request body schema, and response shapes. Instead of scrolling through a 3,000-line YAML file trying to find the endpoint you need, you get a structured, searchable view of the entire API surface.

The parser handles both OpenAPI 3.x and Swagger 2.0 formats. It also accepts raw JSON payloads for simpler use cases—paste in an example response from an API, and the tool infers the schema from the structure. This is useful when you're working with an API that doesn't have a formal spec (which, realistically, is most of them).

2. Mock Response Generation

Once the spec is parsed, you can generate realistic mock responses for any endpoint. The mock data isn't random noise—it uses the field names, types, and constraints from the schema to produce contextually appropriate values. A field called email gets a realistic email address. A field called created_at gets a properly formatted timestamp. An array with minItems: 3 gets at least three entries.

3. Code Snippet Generation

For every parsed endpoint, API Contract Lab generates ready-to-use code in four formats:

Format	Output	Best For
fetch	Native browser fetch with headers, body, and error handling	Frontend JavaScript, modern web apps
curl	Command-line request with all flags and parameters	Quick terminal testing, CI/CD scripts
Python	requests library call with proper headers and JSON handling	Backend scripts, data pipelines, automation
React Query	useQuery/useMutation hook with typed parameters	React applications using TanStack Query

Each snippet is complete—not a skeleton you need to fill in, but a working request with the correct URL, headers, authentication placeholders, and request body. Copy it, paste it into your project, swap in your actual auth token, and it works. The time savings compound fast: on a 20-endpoint API, that's 20 fetch calls you didn't write from scratch.

4. Postman Collection Export

The entire parsed API can be exported as a Postman Collection with one click. Every endpoint becomes a pre-configured request with the correct method, URL, headers, query parameters, and example request bodies. Folders mirror the API's resource structure. Variables are set up for base URL and authentication so you can switch between environments without editing individual requests.

Workflow: From Spec to Working Code

Here's the typical workflow from start to finish:

1. Receive a spec. Your backend team sends an OpenAPI file, or you find a public API with documentation. Copy the spec.
2. Paste and parse. Open API Contract Lab, paste the spec into the input area. The tool immediately breaks down every endpoint, parameter, and response type.
3. Explore endpoints. Browse the parsed endpoints to understand the API surface. Check required vs. optional parameters. Review response schemas.
4. Generate mocks. For the endpoints you're building against, generate mock responses. Use them in your development environment or as test fixtures.
5. Copy code snippets. Grab the fetch or React Query snippet for each endpoint you need. Paste into your codebase. Update the auth token placeholder.
6. Export Postman Collection. Download the complete collection for team-wide API testing. Share with QA, other developers, or keep for your own manual testing.

The entire process takes a few minutes. Without the tool, steps 3 through 6 would each take 15–30 minutes individually.

Supported Input Formats

Input	Versions	Notes
OpenAPI	3.0, 3.1	Full support for paths, schemas, security, components
Swagger	2.0	Automatic conversion to OpenAPI 3.x internally
JSON Schema	Draft 7+	Generates mock data and validates structure
Raw JSON	Any	Schema inferred from structure; best for quick exploration

Privacy and Architecture

API Contract Lab runs entirely in your browser. Your specs, schemas, and generated data never leave your machine unless you explicitly save a project to the cloud (which requires a free Wigley Studios account). This is a deliberate architectural decision: API specifications often contain internal URLs, authentication schemes, and proprietary endpoint structures. Client-side processing means zero data privacy concerns.

If you do create an account, saved projects are stored on the Wigley Studios API and support versioning. You can iterate on a spec, save different versions, and return to any previous state. Sharing is built in—generate a read-only link for teammates who need to reference the parsed spec without accessing your account.

Where It Fits in the Developer Labs Ecosystem

API Contract Lab is one of three tools in Developer Labs, each designed for a different phase of development:

• Brand Token Studio handles the design system layer: colors, typography, spacing, shadows. Define your tokens visually and export as CSS, JSON, or Tailwind config.
• API Contract Lab handles the data layer: understand your API, generate mocks, produce client code, and export testing collections.
• Mock Data Lab handles the content layer: generate realistic structured data from JSON Schema, TypeScript interfaces, or sample JSON. Export as JSON, CSV, or SQL INSERT statements.

Together, the three tools cover the common friction points that slow down the early stages of any project: establishing a visual system, understanding the API you're building against, and populating your development environment with realistic data. Each tool works independently, but the combination eliminates a significant chunk of setup time.