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This module contains a component adding a self-hosted REST API Explorer to LoopBack applications.


npm install --save @loopback/rest-explorer

Basic use

The component should be loaded in the constructor of your custom Application class. Applications scaffolded by recent versions of our lb4 CLI tool have the self-hosted REST API Explorer pre-configured out of the box.

Start by importing the component class:

import {RestExplorerComponent} from '@loopback/rest-explorer';

In the constructor, add the component to your application:


By default, API Explorer is mounted at /explorer. This path can be customized via RestExplorer configuration as follows:

  path: '/openapi/ui',


  path: '/openapi/ui',

Advanced Configuration and Reverse Proxies

By default, the component will add an additional OpenAPI spec endpoint, in the format it needs, at a fixed relative path to that of the Explorer itself. For example, in the default configuration, it will expose /explorer/openapi.json, or in the examples above with the Explorer path configured, it would expose /openapi/ui/openapi.json. This is to allow it to use a fixed relative path to load the spec, to be tolerant of running behind reverse proxies.

You may turn off this behavior in the component configuration, for example:

  useSelfHostedSpec: false,

If you do so, it will try to locate an existing configured OpenAPI spec endpoint of the required form in the REST Server configuration. This may be problematic when operating behind a reverse proxy that inserts a path prefix.

When operating behind a reverse proxy that does path changes, such as inserting a prefix on the path, using the default behavior for useSelfHostedSpec is the simplest option, but is not sufficient to have a functioning Explorer. You will also need to explicitly configure rest.openApiSpec.servers (in your application configuration object) to have an entry that has the correct host and path as seen by the client browser.

Note that in this scenario, setting rest.openApiSpec.setServersFromRequest is not recommended, as it will cause the path information to be lost, as the standards for HTTP reverse proxies only provide means to tell the proxied server (your app) about the hostname used for the original request, not the full original path.

Note also that you cannot use a url-relative path for the servers entry, as the Swagger UI does not support that (yet). You may use a host-relative path however.

Disable Self-Hosted API Explorer

To disable the self-hosted API Explorer, remove the component from the constructor of your custom Application class. Typically the component will be located in ./src/application.ts and consist of two items, for example:

  path: '/openapi/ui',


For some common scenarios, here are recommended configurations to have the explorer working properly. Note that these are not the only configurations that will work reliably, they are just the simplest ones to setup.

Scenario useSelfHostedSpec setServersFromRequest servers
App exposed directly yes either automatic
App behind simple reverse proxy yes yes automatic
App exposed directly or behind simple proxy, with a basePath set yes yes automatic
App exposed directly or behind simple proxy, mounted inside another express app yes yes automatic
App behind path-modifying reverse proxy, modifications known to app1 yes no configure manually as host-relative path, as clients will see it
App behind path-modifying reverse proxy, modifications not known to app2 ? ? ?
App uses custom OpenAPI spec instead of LB4-generated one no depends on reverse-proxy configuration depends on reverse-proxy configuration

1 The modifications need to be known to the app at build or startup time so that you can manually configure the servers list. For example, if you know that your reverse proxy is going to expose the root of your app at /foo/bar/, then you would set the first of your servers entries to /foo/bar. This scenario also cases where the app is using a basePath or is mounted inside another express app, with this same reverse proxy setup. In those cases the manually configured servers entry will need to account for the path prefixes the basePath or express embedding adds in addition to what the reverse proxy does.

2 Due to limitations in the OpenAPI spec and what information is provided by the reverse proxy to the app, this is a scenario without a clear standards-based means of getting a working explorer. A custom solution would be needed in this situation, such as passing a non-standard header from your reverse proxy to tell the app the external path, and custom code in your app to make the app and explorer aware of this.

Customizing Swagger UI Theme

The Explorer UI’s visual style can be customized by configuring the swaggerThemeFile property. Here is the steps to do it:

First, provide your own Swagger-UI theme file in a public folder. For example, in the Todo example application:

Its /public folder is set up as the default home page with url /. Copy a swagger theme file theme-newspaper.css to be under /public.

Then configure the swaggerThemeFile field to be the relative path to home page as /theme-newspaper.css:

export class TodoListApplication extends BootMixin(
) {
  constructor(options: ApplicationConfig = {}) {
    // ...

    // customize the swagger-ui
      // Keep the theme file in the `public` dir of the app
      // If required create a dir and keep the file, just specify the path
      swaggerThemeFile: '/theme-newspaper.css',

    // ...

When the application runs, the explorer template will load the theme-newspaper.css file as its theme.

Here is a repository that contains popular Swagger-UI themes:

Overriding the Swagger UI index.html

For more flexibility, the indexTemplatePath property can be used to allow full customization of Swagger UI configuration options.

indexTemplatePath should be an absolute path to a .html.ejs template.

To get started, download the default index.html.ejs, add /explorer/index.html.ejs to your project, and update the configuration:

  // For example, create a directory "explorer" at the same level
  // as "src" and "node_modules" in your applciation structure
  indexTemplatePath: path.resolve(__dirname, '../explorer/index.html.ejs'),



Run npm test from the root folder.


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