Basic Concepts

API Simulations

API Simulator™ is a versatile tool for easily modeling and running API simulations.


API Simulations are stand-in substitutes that imitate the behavior and data of real APIs or APIs that are yet to be developed.

One can think of API simulations as more powerful and smarter remote stubs and mocks.


An API Simulation consists of a set of simlets. For synchronous request/response type of APIs exposed over HTTP:


A simlet simulates the HTTP response to an HTTP request.

Request Matching

API Simulator inspects the input by applying matching rules. Those matching rules usually look for key values in the input but can also try to match the complete input verbatim.

A matched input is then mapped to the simlet that will produce the simulated output for that input.

There are two options for when no simlet from the simulation matches an input:

  • Use a default fallback simlet, or

  • Forward unrecognized requests to their actual destination and pass back the live responses.

Response Rendering

There are two types of responses with respect to their content: static stubs/mocks and dynamic responses.

Static API response stubs/mocks are canned responses - responses that don’t change between requests for the same simlet.

Dynamic responses produced by a simlet are rendered from a template. The template is comprised of fragments. Special kinds of fragments - placeholders and scriptlets - make it possible to provide dynamic output.

API Simulator renders and returns the appropriate response according to the simlet’s configuration.

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Happy API Simulating!