The OpenAPI specification is a language-agnostic definition format used to describe RESTful APIs. Nest provides a dedicated module which allows generating such a specification by leveraging decorators.


To begin using it, we first install the required dependencies.

$ npm install --save @nestjs/swagger swagger-ui-express

If you use fastify, install fastify-swagger instead of swagger-ui-express:

$ npm install --save @nestjs/swagger fastify-swagger


Once the installation process is complete, open the main.ts file and initialize Swagger using the SwaggerModule class:

import { NestFactory } from '@nestjs/core';
import { SwaggerModule, DocumentBuilder } from '@nestjs/swagger';
import { AppModule } from './app.module';
async function bootstrap() {
const app = await NestFactory.create(AppModule);
const options = new DocumentBuilder()
.setTitle('Cats example')
.setDescription('The cats API description')
const document = SwaggerModule.createDocument(app, options);
SwaggerModule.setup('api', app, document);
await app.listen(3000);

info Hint document (returned by the SwaggerModule#createDocument() method) is a serializable object conforming to OpenAPI Document. Instead of hosting it via HTTP, you could also save it as a JSON/YAML file, and consume it in different ways.

The DocumentBuilder helps to structure a base document that conforms to the OpenAPI Specification. It provides several methods that allow setting such properties as title, description, version, etc. In order to create a full document (with all HTTP routes defined) we use the createDocument() method of the SwaggerModule class. This method takes two arguments, an application instance and a Swagger options object. Alternatively, we can provide a third argument, which should be of type SwaggerDocumentOptions. More on this in the Document options section.

Once we create a document, we can call the setup() method. It accepts:

  1. the path to mount the Swagger UI
  2. an application instance
  3. the document object instantiated above

Now you can run the following command to start the HTTP server:

$ npm run start

While the application is running, open your browser and navigate to http://localhost:3000/api. You should see the Swagger UI.

The SwaggerModule automatically reflects all of your endpoints. Note that the Swagger UI is created using either swagger-ui-express or fastify-swagger, depending on the platform.

info Hint To generate and download a Swagger JSON file, navigate to http://localhost:3000/api-json (swagger-ui-express) or http://localhost:3000/api/json (fastify-swagger) in your browser (assuming that your Swagger documentation is available under http://localhost:3000/api).

warning Warning When using fastify-swagger and helmet, there may be a problem with CSP, to solve this collision, configure the CSP as shown below:

app.register(helmet, {
contentSecurityPolicy: {
directives: {
defaultSrc: [`'self'`],
styleSrc: [`'self'`, `'unsafe-inline'`],
imgSrc: [`'self'`, 'data:', ''],
scriptSrc: [`'self'`, `https: 'unsafe-inline'`],
// If you are not going to use CSP at all, you can use this:
app.register(helmet, {
contentSecurityPolicy: false,

title: Document options

When creating a document, it is possible to provide some extra options to finetune the library's behavior. These options should be of type SwaggerDocumentOptions, which can be the following:

export interface SwaggerDocumentOptions {
* List of modules to include in the specification
include?: Function[];
* Additional, extra models that should be inspected and included in the specification
extraModels?: Function[];
* If `true`, swagger will ignore the global prefix set through `setGlobalPrefix()` method
ignoreGlobalPrefix?: boolean;
* If `true`, swagger will also load routes from the modules imported by `include` modules
deepScanRoutes?: boolean;
* Custom operationIdFactory that will be used to generate the `operationId`
* based on the `controllerKey` and `methodKey`
* @default () => controllerKey_methodKey
operationIdFactory?: (controllerKey: string, methodKey: string) => string;

For example, if you want to make sure that the library generates operation names like createUser instead of UserController_createUser, you can set the following:

const document = SwaggerModule.createDocument(app, options, {
operationIdFactory: (
controllerKey: string,
methodKey: string
) => methodKey;


A working example is available here.