OpenAPI Generator

Build a clean OpenAPI 3.0 specification from a simple form. Define your API info, server, endpoints, parameters, and responses, then export as YAML or JSON.

API Info

Server

Endpoints

Method
Path
Summary
Tag
Description
Parameters
Responses

Generated OpenAPI Spec

Live output updates as you edit the form.

openapi: 3.0.3
info:
  title: Sample API
  version: 1.0.0
  description: A sample OpenAPI specification generated with DevToolEasy.
servers:
  - url: "https://api.example.com/v1"
    description: Production server
paths:
  /users:
    get:
      tags:
        - users
      summary: List users
      description: Returns a list of users
      parameters:
        - name: limit
          in: query
          required: false
          description: Max items to return
          schema:
            type: integer
      responses:
        200:
          description: Successful response
        400:
          description: Bad request

Paste into Swagger Editor or import into Postman, Stoplight, or Redocly to preview and validate.

About OpenAPI Generator

The OpenAPI Generator helps you build a valid OpenAPI 3.0 (formerly Swagger) specification without writing YAML or JSON by hand. OpenAPI is the industry-standard format for describing REST APIs. It defines endpoints, parameters, request bodies, and responses in a machine-readable way that tools like Swagger UI, Postman, Redoc, and code generators can consume.

Fill out the form with your API information, server URL, and each endpoint you want to document. The tool compiles your input into a clean OpenAPI spec you can copy, download, or paste into any OpenAPI-compatible tool. Everything runs locally in your browser — nothing is sent to a server.

How to Use OpenAPI Generator

  1. Enter your API title, version, and a short description under API Info.
  2. Add your production or staging server URL and an optional description.
  3. Click Add Endpoint to create a new path. Select HTTP method (GET, POST, PUT, PATCH, DELETE) and enter the path (e.g. /users/{id}).
  4. Write a short summary, optional tag (used for grouping), and a longer description.
  5. Add parameters with name, location (query, path, or header), type, and whether they are required.
  6. For POST, PUT, and PATCH, paste a JSON example into the request body field.
  7. Define expected responses with HTTP status codes and a description (e.g. 200 OK, 404 Not Found).
  8. Toggle between YAML and JSON output, then copy or download your completed OpenAPI specification.

Common Use Cases

API Documentation

Generate specs to feed into Swagger UI or Redoc for interactive developer documentation.

Client SDK Generation

Use tools like openapi-generator-cli to build TypeScript, Python, Java, or Go clients from your spec.

Postman Collection Import

Export OpenAPI JSON and import into Postman to bootstrap a request collection instantly.

Contract-First Development

Define the API contract before writing code so backend and frontend teams can work in parallel.

Mock Servers

Plug the spec into Prism, Stoplight, or MockServer to spin up realistic mock APIs for testing.

API Governance & Review

Share a single YAML file in pull requests to review API changes with stakeholders.

Frequently Asked Questions

What is OpenAPI?

OpenAPI (formerly Swagger) is a standard, language-agnostic specification for describing HTTP APIs. It lets humans and machines understand the capabilities of a service without access to source code.

What version of OpenAPI does this tool generate?

The generator outputs OpenAPI 3.0.3 specifications, which are compatible with Swagger UI, Redoc, Postman, Stoplight, openapi-generator-cli, and most other OpenAPI tooling.

Should I use YAML or JSON?

YAML is more compact and easier to read or edit manually, making it popular for hand-written specs. JSON is easier for programs to parse and is the native format for many tools. Both formats are semantically identical — pick based on your workflow.

Is my API data uploaded anywhere?

No. The generator runs entirely in your browser. Your API title, paths, and example bodies never leave your device.

How do I preview my OpenAPI spec?

Paste the output into the Swagger Editor at editor.swagger.io or import it into tools like Redocly, Postman, or Stoplight for interactive preview.

Can I add path parameters?

Yes. Write them inside curly braces in the path, for example /users/{id}, then add a parameter with location set to path. Path parameters are always required.

Can I add authentication or security schemes?

This builder focuses on paths, parameters, and responses. For full security schemes (Bearer, OAuth2, API Key), you can add a components.securitySchemes block manually after export.

Can I use this with openapi-generator-cli to generate clients?

Yes. Save the output as openapi.yaml or openapi.json, then run openapi-generator-cli generate -i openapi.yaml -g typescript-fetch -o ./client to produce a client SDK.