# Introduction

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

Simply open the bootstrap.ts file and initialize Swagger using the SwaggerModule class:

import { DanetApplication } from 'https://deno.land/x/danet/mod.ts';
import { SwaggerModule, SpecBuilder } from 'https://deno.land/x/danet_swagger/mod.ts';
import { AppModule } from './app.module';

async function bootstrap() {
  const application = new DanetApplication();
  await application.init(AppModule);
  const spec = new SpecBuilder()
    .setTitle('Todo')
    .setDescription('The todo API')
    .setVersion('1.0')
    .build();
  const document = await SwaggerModule.createDocument(application, spec);
  SwaggerModule.setup('api', application, document);
  return application;
}

The SpecBuilder 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.

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:

$ deno task launch-server

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.