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This package provides data validation within an Express or Koa app according to a Swagger/OpenAPI definition. It uses Ajv under the hood for validation.

Table of Contents


Install using the node package registry:

npm install --save express-ajv-swagger-validation

Then import the module in your code:

const swaggerValidation = require('express-ajv-swagger-validation');



This middleware function validates the request body, headers, path parameters and query parameters according to the paths definition of the swagger file. Make sure to use this middleware inside a route definition in order to have req.route.path assigned to the most accurate express route.

express-ajv-swagger-validation.init(pathToSwaggerFile, options)

Initialize the middleware using a swagger definition. The function executes synchronously and does not return anything.

  • pathToSwaggerFile: Path to the swagger definition.
  • options: Additional options for the middleware (see below).


Options currently supported:

  • framework - Defines in which framework the middleware is working ('koa' or 'express'). As default, set to 'express'.

  • formats - Array of formats that can be added to ajv configuration, each element in the array should include name and pattern.

    formats: [
        { name: 'double', pattern: /\d+\.(\d+)+/ },
        { name: 'int64', pattern: /^\d{1,19}$/ },
        { name: 'int32', pattern: /^\d{1,10}$/ }
  • keywords - Array of keywords that can be added to ajv configuration, each element in the array can be either an object or a function. If the element is an object, it must include name and definition. If the element is a function, it should accept ajv as its first argument and inside the function you need to call ajv.addKeyword to add your custom keyword

  • beautifyErrors- Boolean that indicates if to beautify the errors, in this case it will create a string from the Ajv error.

    • Examples:
      • query/limit should be <= 100 - query param
      • path/petId should NOT be shorter than 3 characters - path param not in format
      • body/[0].test.field1 should be string - Item in an array body
      • body/test should have required property 'field1' - nested field
      • body should have required property 'name' - Missing field in body

    You can see more examples in the tests.

  • firstError - Boolean that indicates if to return only the first error.

  • makeOptionalAttributesNullable - Boolean that forces preprocessing of Swagger schema to include 'null' as possible type for all non-required properties. Main use-case for this is to ensure correct handling of null values when Ajv type coercion is enabled

  • ajvConfigBody - Object that will be passed as config to new Ajv instance which will be used for validating request body. Can be useful to e. g. enable type coercion (to automatically convert strings to numbers etc). See Ajv documentation for supported values.

  • ajvConfigParams - Object that will be passed as config to new Ajv instance which will be used for validating request body. See Ajv documentation for supported values.

  • contentTypeValidation - Boolean that indicates if to perform content type validation in case consume field is specified and the request body is not empty.

  • expectFormFieldsInBody - Boolean that indicates whether form fields of non-file type that are specified in the schema should be validated against request body (e. g. Multer is copying text form fields to body)

  • errorFormatter - optional custom function that will be invoked to create a validation error that will be thrown if Ajv validation fails. Function should accept two parameters: (errors, middlewareOptions) and return an error that will be thrown.

Usage Example


const app = express();
app.get('/pets', swaggerValidator.validate, (req, res, next) => {
    return res.json({ result: 'OK' });
});'/pets', swaggerValidator.validate, (req, res, next) => {
    return res.json({ result: 'OK' });
app.get('/pets/:petId', swaggerValidator.validate, (req, res, next) => {
    return res.json({ result: 'OK' });
app.use((err, req, res) => {
    if (err instanceof swaggerValidator.InputValidationError) {
        return res.status(400).json({ more_info: JSON.stringify(err.errors) });
const server = app.listen(serverPort, () => {});


'use strict';
const Koa = require('koa');
const Router = require('koa-router');
const bodyParser = require('koa-bodyparser');
const inputValidation = require('../../src/middleware');
let app = new Koa();
let router = new Router();
module.exports = inputValidation.init('test/pet-store-swagger.yaml', {framework: 'koa'});
router.get('/pets', inputValidation.validate, async (ctx, next) => {
    ctx.status = 200;
    ctx.body = { result: 'OK' };
});'/pets', inputValidation.validate, async (ctx, next) => {
    ctx.status = 200;
    ctx.body = { result: 'OK' };
router.get('/pets/:petId', inputValidation.validate, async (ctx, next) => {
    ctx.status = 200;
    ctx.body = { result: 'OK' };
router.put('/pets', inputValidation.validate, async (ctx, next) => {
    ctx.status = 200;
    ctx.body = { result: 'OK' };
return app;

Important Notes

Schema Objects

It is important to set the type property of any Schema Objects explicitly to object. Although it isn't required in the OpenAPI specification, it is necessary in order for Ajv to work correctly.

Multipart/form-data (files)

Multipart/form-data (files) support is based on express/multer.

Koa support

When using this package as middleware for koa, the validations errors are being thrown.

Koa packages

This package supports Koa servers that use koa-router, koa-bodyparser and koa-multer.

Known Issues with OpenAPI 3

  • Inheritance with a discriminator is supported only if the ancestor object is the discriminator.
  • The discriminator support in the inheritance chain stops when getting to a child without a discriminator (a leaf in the inheritance tree), meaning a child without a discriminator cannot point to another child with a discriminator.

Running Tests

The tests use mocha, istanbul and mochawesome. Run them using the node test script:

npm test


npm i express-ajv-swagger-validation

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