Extended validator for Middy

Usage no npm install needed!

<script type="module">
  import middyExtendedValidator from 'https://cdn.skypack.dev/middy-extended-validator';



version downloads

Middy 2.0+ middleware that extends the included validator middleware.


  • Extended validation error messages (with details)
  • Allow mounting a JSON schema file under a body root property. This allow using the JSON schema file to server as schema for the actual request not just the request as received in a lambda function.

Getting Started

Installing middy-extended-validator

npm install --save @middy/core
npm install --save middy-extended-validator


const middy = require('@middy/core');
const httpErrorHandler = require('@middy/http-error-handler');
const jsonBodyParser = require('@middy/http-json-body-parser');
const validator = require('middy-extended-validator');

const schema = require('some-json-schema.json');

const handler = async event => {
  // do something with event.body...

  const statusCode = 200;
  const body = JSON.stringify({ message: 'something' })
  return {

module.exports.handler = middy(handler)
  .use(validator({ inputSchema: schema, mountSchemaAtBody: true, detailedErrors: true }))


The middleware accepts the following options:


The mountSchemaAtBody takes the inputSchema and mounts its properties under a body property in the root.

Allows using a schema such as:

const schema = {
  type: 'object',
  properties: {
    foo: { type: 'string' }
  required: ['foo'],

and turns it into this:

const schema = {
  type: 'object',
  properties: {
    body: { type: 'object' },
    properties: {
      foo: { type: 'string' }
    required: ['foo'],
  require: ['body']

which corresponds to how the event actually looks as received in the lambda function.

This is especially useful if the schema is defined externally and also used for generating documentation for example.


The default message returned by the included validator is just that validation failed (Event object failed validation).

The detailedErrors option instead returns a http-errors compatible object that includes both a message as well as a details property which are both returned to the client as JSON.

For example:

  "details:" "should have required property foo",
  "message": "Event object failed validation"