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Lightweight request/response validation middleware based on swagger/OpenAPI schema

Swagger Express Validator

Build Status

swagger-express-validator is a lightweight middleware for request/response validation based on
OpenAPI v2.0 (aka swagger) specification.

The main difference of this package to alternatives like
swagger-tools is that this package is very
configurable and only concentrates on validation against provided schema. You can choose the
behavior of invalid validation like returning a 500 or just logging an error to your logger.


  • express ^4.0.0
  • body-parser ^1.0.0


  • Configurable validation behavior
  • Fastest available JSON schema validation based on ajv library
  • Optional validations for either request parameters or response values
  • Independent from express application structure. This is a simple drop-in middleware without additional
    alterations to your swagger definitions or application routing.
  • Support for nullable field validation though x-nullable attribute


Start using this library with npm install swagger-express-validator --save

Sample use

To set up simple validation for your requests and responses:

const util = require('util');
const express = require('express');
const bodyParser = require('body-parser');
const validator = require('swagger-express-validator');
const schema = require('./api-schema.json');

const server = express();

const opts = {
  schema, // Swagger schema
  preserveResponseContentType: false, // Do not override responses for validation errors to always be JSON, default is true
  returnRequestErrors: true, // Include list of request validation errors with response, default is false
  returnResponseErrors: true, // Include list of response validation errors with response, default is false
  validateRequest: true,
  validateResponse: true,
  requestValidationFn: (req, data, errors) => {
    console.log(`failed request validation: ${req.method} ${req.originalUrl}\n ${util.inspect(errors)}`)
  responseValidationFn: (req, data, errors) => {
    console.log(`failed response validation: ${req.method} ${req.originalUrl}\n ${util.inspect(errors)}`)

server.use('/status', (req, res) => {
    status: 'OK',
server.use((err, req, res, next) => {

return server.listen(3000);

Ajv configuration

swagger-express-validator uses Ajv for schema validation under the hood. You can tweak many validation parameters by passing Ajv configuration overrides:

  preserveResponseContentType: false,
  returnRequestErrors: true,
  returnResponseErrors: true,
  validateRequest: true,
  validateResponse: true,
  ajvRequestOptions: {
    coerceTypes: true,
  ajvResponseOptions: {
    coerceTypes: true,

See Ajv documentation for supported values.


To see debug output use DEBUG=swagger-express-validator as an environmental variable when starting
your project, eg.: DEBUG=swagger-express-validator node server.js. To gain more insights
on how this works see documentation of debug library




Special thanks to @bgaluszka for initial inspiration 🙂

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Posted in Development