API Simulator for Easy and Realistic API Simulations

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Applications Heavily Depend on APIs



It is common for an application to depend on the APIs of a dozen or more other applications and components.


These direct dependencies in turn have their own API dependencies, which may depend on even more APIs and so on...

api dependencies diagram

Problems with API Dependencies Hinder Testing and Development

unavailable api dependencies

Testing and development come to a halt when any one of the direct and transitive API dependencies is needed but unavailable.

Development of API Clients can be at standstill waiting for the delivery of new APIs.

External APIs charge pay-per-transaction fees even in non-production environments.

Often times API dependencies enforce rate limiting making performance testing impossible.

The Solution? API Simulations!

API Simulations imitate real APIs or APIs not built yet



API Simulations mimic the direct dependencies.


An API Simulation behaves and outputs static and dynamic data if it was "the real deal".


API Simulations are always available and every time with the right test data.

api simulations diagram

News and Announcements

API Simulator 1.0.0 Released!

April 20, 2018

What a milestone! We are very pleased to announce the release of API Simulator version 1.0.0. Read more…

API Simulator 0.9.0 Released

March 23, 2018

This release quickly follows the release of the Simula Template Engine. The YAML DSL now allows defining parameters from CSV data sources and SQL data stores, configuring JSON, URL, XML, and HTML encoders for output values, and more. Read the details…

Introducing the Simula Template Engine

March 9, 2018

API Simulator release 0.8.2 is out and it makes available the all-new Simula Template Engine for API simulations response templating. Modeling API Simulations and configuring dynamic responses using intuitive YAML DSL (Domain Specific Language) is now easier and more flexible than ever before. Read more…

API Simulator 0.7.0 Released - YAML DSL for API Simulation Modeling

December 31, 2017

What a great way to end 2017! Modeling API Simulations via configuration for the Standalone API Simulator is now easier than ever with our new YAML-based DSL (Domain Specific Language). Read more…

API Simulator 0.6.2 Released

November 14, 2017

This release gets the Embedded API Simulator closer to supporting all the features of the standalone edition. Read more…

API Simulator 0.6.1 Released

November 1, 2017

This release adds to the Embedded API Simulator support for TLS, which makes it possible to simulate APIs invoked over HTTPS. Read more…

Embedded HTTP API Simulator is Here!

October 7, 2017

It is a great day! You've asked and we delivered - embedded API Simulator you can start, stop, and use to simulate HTTP APIs from within your applications and tests. Built on the standalone API Simulator's foundation, the embedded API Simulator also offers an intuitive and simple to use Java DSL (Domain-Specific Language) for defining simulations and their simlets. Read more…

We invite you to learn more about API Simulator, download it, and run the examples. Why not even create API simulations to help your own testing and development?

Let us know what you think at [feedback at APISimulator.com]. Many thanks for your interest and support!

Happy API Simulating!