express-zod-openapi-autogen

This repository provides (relatively) un-opinionated utility methods for creating Express APIs that leverage Zod for request and response validation and auto-generate OpenAPI documentation.

Requirements

• Express@^5.0
• Zod@^3.14

Basic Use

In your route files, wrap each route handler in openAPIRoute. The tag, summary, and description determine how the route is grouped and presented in the OpenAPI schema.

• The params, query, body and response are Zod schemas.

• The openAPIRoute middleware will automatically validate that the incoming data matches your schemas and return 400 errors if required fields are missing, etc. Your route handler will receive typed fields (req.query will match your Zod schema) and you can trust that the data matches the schema.

• The response schema is not required, but OpenAPI routes missing a response schema are documented as returning 204 No Content. If you provide a response schema, the Express res.json is typed to expect the schema. When NODE_ENV=development, the openAPIRoute middleware will console.warn if your response data does not align with your response schema.

• If you omit one of the Zod schemas, no validation is performed and you receive the untyped data in your route handler.

router.get(
  '/users/:id',
  openAPIRoute(
    {
      tag: 'Users',
      summary: 'This is how you receive a specific user',
      description: 'Longer form details about the route',
      params: z.object({ id: z.string() }),
      query: z.object({ debugInfo: z.boolean().optional() }),
      response: UserSchema,
    },
    async (req, res) => {
      ...
    }
  )
);

Create a folder to hold your Zod schemas (eg: src/schemas), and export common types you plan to use repeatedly. For example, in our project we have UserSchema. Some APIs return UserSchema and others return z.array(UserSchema).

We'll pass a reference to these schemas to the OpenAPI generator, allowing it to define them as OpenAPI component schemas and reference them in our API route definitions.

In your Express application's app.ts file, load your route files containing public routes into an array, and pass them to buildOpenAPIDocument to create an OpenAPI schema. Note that buildOpenAPIDocument will throw errors if your Zod schemas are incomplete or cannot be translated to OpenAPI schemas.

import { buildOpenAPIDocument } from 'express-zod-openapi-autogen';
import swaggerUI from 'swagger-ui-express';

const PublicAPIs = [
  require('./routes/users').default,
  require('./routes/session').default,
];

// Attach API routes
for (const router of PublicAPIs) {
  app.use(`${prefix}/api`, router);
}

// Public documentation (auto-generated for all routes above this line)
try {
  const doc = buildOpenAPIDocument(PublicAPIs, ['src/schemas'], {
    openapi: '3.0.0',
    servers: [{ url: `https://server.com/api` }],
    info: {
      version: '1.0.0',
      title: 'My API',
      description: `Welcome to the My API!`,
    },
  });
  app.get(`/openapi.json`, (req, res) => res.json(doc));
  app.use(`/openapi`, swaggerUI.serve, swaggerUI.setup(doc));
} catch (err) {
  console.error(err);
}

Implementation Notes

• Unless you use middleware that converts query parameters to other data types, you may find that ?option=false and ?option=100 are string values when your Zod schemas are validated. You can fix this by adding middleware that coerces these values to numbers/booleans, or by changing your expected Zod type:

  export const OptionalQueryNumber = z
    .union([z.string(), z.number()])
    .optional()
    .openapi({ type: 'number' });

• If you'd like to provide example values, custom types, or descriptions for your Zod schemas, you can do so by chaining calls to z.openapi (shown in the example above). Note that .openapi({example: ...}) can be used on both individual fields and also on entire objects.

• If you use z.any(), you may need to chain a call to z.openapi to specify what type should appear in the OpenAPI specification, since 'any' is not a valid OpenAPI type.