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Author image Jan Henning Thorsen
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Mojolicious::Plugin::OpenAPI::Guides::OpenAPIv2 - Mojolicious <3 OpenAPI v2 (Swagger)


This guide will give you an introduction to how to use Mojolicious::Plugin::OpenAPI with OpenAPI version v2.



This plugin reads an OpenAPI specification and generate routes and input/output rules from it. See JSON::Validator for supported schema file formats.

    "swagger": "2.0",
    "info": { "version": "1.0", "title": "Some awesome API" },
    "basePath": "/api",
    "paths": {
      "/pets": {
        "get": {
          "operationId": "getPets",
          "x-mojo-name": "get_pets",
          "x-mojo-to": "pet#list",
          "summary": "Finds pets in the system",
          "parameters": [
            {"in": "body", "name": "body", "schema": {"type": "object"}},
            {"in": "query", "name": "age", "type": "integer"}
          "responses": {
            "200": {
              "description": "Pet response",
              "schema": {
                "type": "object",
                "properties": {
                  "pets": {
                    "type": "array",
                    "items": { "type": "object" }

The complete HTTP request for getting the "pet list" will be GET /api/pets The first part of the path ("/api") comes from basePath, the second part comes from the keys under paths, and the HTTP method comes from the keys under /pets.

The different parts of the specification can also be retrieved as JSON using the "OPTIONS" HTTP method. Example:

  OPTIONS /api/pets
  OPTIONS /api/pets?method=get

Note that the use of "OPTIONS" is EXPERIMENTAL, and subject to change.

Here are some more details about the different keys:

  • swagger and info

    These two sections are required to make the specification valid. Check out https://github.com/OAI/OpenAPI-Specification/blob/master/versions/2.0.md for a complete reference to the specification.

  • host, schemes, consumes, produces, security and securityDefinitions

    These keys are currently not in use. "host" will be replaced by the "Host" header in the request. The rest of the keys are currently not in use.

    Submit an issue if you have ideas on what to use these keys for.

  • basePath

    The basePath will also be used to add a route that renders back the specification either as JSON or HTML. Examples:

    • http://example.com/api.html

      Retrieve the expanded version of the API in human readable format. The formatting is currently a bit rough, but should be easier than reading the JSON spec.

    • http://example.com/api.json

      Retrieve the expanded version of the API, useful for JavaScript clients and other client side applications.

  • parameters and responses

    parameters and responses will be used to define input and output validtion rules, which is used by "openapi.input" in Mojolicious::Plugin::OpenAPI and when rendering the response back to the client, using render(openapi => ...).

    Have a look at "RENDERER" in Mojolicious::Plugin::OpenAPI for more details about output rendering.

  • operationId and x-mojo-name

    See "Route names".

  • x-mojo-placeholder

    x-mojo-placeholder can be used inside a parameter definition to instruct Mojolicious to parse a path part in a certain way. Example:

      "parameters": [
          "x-mojo-placeholder": "#",
          "in": "path",
          "name": "email",
          "type": "string"

    See Mojolicious::Guides::Routing for more information about "standard", "relaxed" and "wildcard" placeholders. The default is to use the "standard" ("/:foo") placeholder.

  • x-mojo-to

    The non-standard part in the spec above is "x-mojo-to". The "x-mojo-to" key can be either a plain string, object (hash) or an array. The string and hash will be passed directly to "to" in Mojolicious::Routes::Route, while the array ref will be flatten. Examples:

      "x-mojo-to": "pet#list"
      "x-mojo-to": {"controller": "pet", "action": "list", "foo": 123}
      $route->to({controller => "pet", action => "list", foo => 123);
      "x-mojo-to": ["pet#list", {"foo": 123}, ["format": ["json"]]]
      $route->to("pet#list", {foo => 123});
      $route->pattern->constraints->{format} = ["json"];


  package Myapp;
  use Mojo::Base "Mojolicious";

  sub startup {
    my $app = shift;
    $app->plugin("OpenAPI" => {url => $app->home->rel_file("myapi.json")});


The first thing in your code that you need to do is to load this plugin and the "Specification". See "register" in Mojolicious::Plugin::OpenAPI for information about what the plugin config can be.

See also "SYNOPSIS" in Mojolicious::Plugin::OpenAPI for example Mojolicious::Lite application.


  package Myapp::Controller::Pet;
  use Mojo::Base "Mojolicious::Controller";

  sub list {

    # Do not continue on invalid input and render a default 400
    # error document.
    my $c = shift->openapi->valid_input or return;

    # You might want to introspect the specification for the current route
    my $spec = $c->openapi->spec;
    unless ($spec->{'x-opening-hour'} == (localtime)[2]) {
      return $c->render(openapi => [], status => 498);

    my $age  = $c->param("age");
    my $body = $c->req->json;

    # $output will be validated by the OpenAPI spec before rendered
    my $output = {pets => [{name => "kit-e-cat"}]};
    $c->render(openapi => $output);


The input will be validated using "openapi.valid_input" in Mojolicious::Plugin::OpenAPI while the output is validated through then openapi handler.

Route names

Routes will get its name from either "x-mojo-name" or from "operationId" if defined in the specification.

The route name can also be used the other way around, to find already defined routes. This is especially useful for Mojolicious::Lite apps.

Note that if spec_route_name then all the route names will have that value as prefix:

  spec_route_name            = "my_cool_api"
  operationId or x-mojo-name = "Foo"
  Route name                 = "my_cool_api.Foo"

You can also set "x-mojo-name" in the spec, instead of passing spec_route_name to plugin():

    "swagger": "2.0",
    "info": { "version": "1.0", "title": "Some awesome API" },
    "x-mojo-name": "my_cool_api"

Default response schema

A default response definition will be added to the API spec, unless it's already defined. This schema will at least be used for invalid input (400 - Bad Request) and invalid output (500 - Internal Server Error), but can also be used in other cases.

See "default_response_codes" in Mojolicious::Plugin::OpenAPI and "default_response_name" in Mojolicious::Plugin::OpenAPI for more details on how to configure these settings.

The response schema will be added to your spec like this, unless already defined:

    "definitions": {
      "DefaultResponse": {
        "type":     "object",
        "required": ["errors"],
        "properties": {
          "errors": {
            "type":  "array",
            "items": {
              "type":       "object",
              "required":   ["message"],
              "properties": {"message": {"type": "string"}, "path": {"type": "string"}}

The "errors" key will contain one element for all the invalid data, and not just the first one. The useful part for a client is mostly the "path", while the "message" is just to add some human readable debug information for why this request/response failed.

Rendering binary data

Rendering assets and binary data should be accomplished by using the standard Mojolicious tools:

  sub get_image {
    my $c = shift->openapi->valid_input or return;
    my $asset = Mojo::Asset::File->new(path => "image.jpeg");



Mojolicious::Plugin::OpenAPI, https://openapis.org/specification.