mountebank

1.4.954 verified Fri May 01 auth: no javascript

mountebank is the first open source tool for cross-platform, multi-protocol test doubles over the wire. It supports HTTP, HTTPS, TCP (text and binary), and SMTP protocols. Current stable version is 2.9.4, published under the @mbtest/mountebank package (was formerly mountebank). The community-driven project requires Node.js >=20. It offers mock verification, stubbing with advanced predicates, JavaScript injection, and record-playback through proxying, distinguishing itself from alternatives like WireMock by supporting multiple protocols and being fully open source without platform constraints. Releases are maintained by the mountebank-testing organization.

Common errors

error Error: Cannot find module 'mountebank' ↓

cause Using outdated package name mountebank instead of @mbtest/mountebank.

fix

Run npm install @mbtest/mountebank and update imports to '@mbtest/mountebank'.

error TypeError: mb.spawn is not a function ↓

cause Incorrect import of 'spawn' from '@mbtest/mountebank'.

fix

Use import { spawn } from '@mbtest/mountebank'; then const mb = spawn({...});.

error SyntaxError: The requested module '@mbtest/mountebank' does not provide an export named 'default' ↓

cause Using default import when package only exports named exports.

fix

Use named import: import { spawn, Imposter } from '@mbtest/mountebank';

Warnings

breaking Package name changed from mountebank to @mbtest/mountebank in v2.9.2. Update install commands and imports accordingly. ↓

fix Use `npm install --save-dev @mbtest/mountebank` and update import paths to '@mbtest/mountebank'.

breaking Minimum Node.js version updated to 20 in v2.9.4. ↓

fix Upgrade Node.js to version 20 or higher.

deprecated mountebank v1.x (npm package mountebank) is deprecated; use @mbtest/mountebank v2.x. ↓

fix Migrate to @mbtest/mountebank v2.9.4.

gotcha Node 24 required for Docker image in v2.9.4; local install works with Node 20+. ↓

fix Use Node 20+ for local development; Docker users must use Node 24 image.

breaking nodemailer dependency updated to v8 in v2.9.4, which may break custom email handling. ↓

fix Update SMTP-related code to be compatible with nodemailer v8.

Install

npm install mountebank-test

yarn add mountebank-test

pnpm add mountebank-test

Imports

mb
wrong
```
import mb from 'mountebank';
```
correct
```
import { spawn } from '@mbtest/mountebank';
const mb = spawn({ port: 2525 });
```
Since v2.9.2 the package name is @mbtest/mountebank. The CLI command is 'mb', imported via spawn function for programmatic usage.

MountebankClient

wrong

import MountebankClient from 'mountebank';

correct

import { MountebankClient } from '@mbtest/mountebank/client';

Client class for API interaction; path may vary; check docs.

Imposter

wrong

const Imposter = require('mountebank').Imposter;

correct

import { Imposter } from '@mbtest/mountebank';

ESM module; CommonJS require is deprecated.

Quickstart

Creates and starts an HTTP imposter on port 3000 with a stub responding to /api/data.

import { spawn, Imposter, Stub } from '@mbtest/mountebank';

const mb = spawn({ port: 2525, loglevel: 'debug' });
const imposter = new Imposter({ port: 3000, protocol: 'http', name: 'test' });
const stub = new Stub().withPredicate({ equals: { path: '/api/data' } }).withResponse({ statusCode: 200, body: { data: 'success' } });
await mb.use(imposter);
await mb.start();
console.log('mountebank running on port 2525');
// ... use imposter ...
await mb.close();