Get unlimited public & private packages + package-based permissions with npm Pro.Get started »


0.5.1 • Public • Published


Build Status Coverage Status npm version Try on RunKit

Express middleware to validate requests based on an OpenAPI 3.0 document. OpenAPI specification was called the Swagger specification before version 3.


Install this package with npm or yarn:

npm install --save express-openapi-validate
# or 
yarn add express-openapi-validate

Then use the validator like this:


const fs = require("fs");
const express = require("express");
const { OpenApiValidator } = require("express-openapi-validate");
const jsYaml = require("js-yaml");
const app = express();
const openApiDocument = jsYaml.safeLoad(
  fs.readFileSync("openapi.yaml", "utf-8"),
const validator = new OpenApiValidator(openApiDocument);"/echo", validator.validate("post", "/echo"), (req, res, next) => {
  res.json({ output: req.body.input });
app.use((err, req, res, next) => {
  const statusCode = err.statusCode || 500;
    error: {
      message: err.message,
const server = app.listen(3000, () => {
  console.log("Listening on", server.address());

Or using match():

// Apply to all requests
// On each request validator.validate("post", "/echo") is called automatically,
// if it has a matching specification in the OpenAPI schema"/echo", (req, res, next) => {
  res.json({ output: req.body.input });


openapi: 3.0.1
  title: Example API with a single echo endpoint
  version: 1.0.0
      type: object
          type: object
              type: string
              type: string
              type: array
                type: object
            - name
            - message
        - error
      description: Default error response with error object
            $ref: "#/components/schemas/Error"
      description: Echo input back
              type: object
                  type: string
                - input
          description: Echoed input
                type: object
                    type: string
          $ref: "#/components/responses/error"

Supported features

Currently unsupported features

Public API

class OpenApiValidator

const { OpenApiValidator } = require("express-openapi-validate");

The main class of this package. Creates JSON schema validators for the given operations defined in the OpenAPI document. In the background Ajv is used to validate the request.

constructor(openApiDocument: OpenApiDocument, options: ValidatorConfig = {}))

Creates a new validator for the given OpenAPI document.

options parameter is optional. It has the following optional fields:

  ajvOptions: Ajv.Options;

You can find the list of options accepted by Ajv from its documentation. The formats object passed to Ajv will be merged with additional OpenAPI formats supported by this library.

validate(method: Operation, path: string): RequestHandler

Returns an express middleware function for the given operation. The operation matching the given method and path has to be defined in the OpenAPI document or this method throws.

The middleware validates the incoming request according to the parameters and requestBody fields defined in the Operation Object. If the validation fails the next express function is called with an ValidationError.

See the Parameter Object and Request Body Object sections of the OpenAPI specification for details how to define schemas for operations.

method must be one of the valid operations of an OpenAPI Path Item Object: "get" | "put" | "post" | "delete" | "options" | "head" | "patch" | "trace".

RequestHandler is an express middleware function with the signature (req: Request, res: Response, next: NextFunction): any;.

match(): RequestHandler

Returns an express middleware function which calls validate() based on the request method and path. Using this function removes the need to specify validate() middleware for each express endpoint individually.

Note that behaviour is different to validate() for routes where no schema is specified: validate() will throw an exception if no matching route specification is found in the OpenAPI schema. match() will not throw an exception in this case; the request is simply not validated. Be careful to ensure you OpenAPI schema contains validators for each endpoint if using match().

The following examples achieve the same result:

// Using validate()"/echo", validator.validate("post", "/echo"), (req, res, next) => {
  res.json({ output: req.body.input });
// Using match()
app.use(validator.match());"/echo", (req, res, next) => {
  res.json({ output: req.body.input });

validateResponse(method: Operation, path: string): (res: any) => void

Creates a function for the given operation that can be used to validate responses. Response validation is meant to be used in tests and not in production code. See below for example usage.

For documentation of the method and path parameters see validate.

res is expected to have the shape { statusCode: number, body: {}, headers: {}}. The statusCode field can also be called status and the body field can be called data. This means that response objects from most request libraries should work out of the box.

If validation fails the validation function throws a ValidationError. Otherwise it returns undefined.

Example usage when using Jest and SuperTest:

import { OpenApiValidator } from "express-openapi-validate";
import fs from "fs";
import jsYaml from "js-yaml";
import request from "supertest";
import app from "./app";
const openApiDocument = jsYaml.safeLoad(
  fs.readFileSync("openapi.yaml", "utf-8"),
const validator = new OpenApiValidator(openApiDocument);
test("/echo responses", async () => {
  const validateResponse = validator.validateResponse("post", "/echo");
  let res = await request(app)
  res = await request(app)
    .send({ input: "Hello!" });

class ValidationError extends Error

const { ValidationError } = require("express-openapi-validate");

This error is thrown by OpenApiValidator#validate when the request validation fails. It contains useful information about why the validation failed in human-readable format in the .message field and in machine-readable format in the .data array.

You can catch this error in your express error handler and handle it specially. You probably want to log the validation error and pass the errors to the client.

message: string

Human-readable error message about why the validation failed.

statusCode: number = 400

This field is always set to 400. You can check this field in your express error handler to decide what status code to send to the client when errors happen.

data: ErrorObject[]

Machine-readable array of validation errors. Ajv Error Objects documentation contains a list of the fields in ErrorObject.


npm i express-openapi-validate

DownloadsWeekly Downloads






Unpacked Size

160 kB

Total Files


Last publish


  • avatar