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Visualize your Observables
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RxFiddle is a debugger for Reactive Extensions (Rx).


  • visualises structure of Observables in graph diagram,
  • visualises construction of and data flow through Observable sequences in Marble Diagrams,
  • supports live fiddling with input streams,
  • generates tests for Observable sequences.


RxFiddle works by means of a visualizer and collectors which can parse syntax and instrument (compiled) code to collect the lifecycle of Observables:

  • creation of Observable sequences
  • subscriptions in a Observable sequence
  • onNext, onError and onComplete events in Observable sequence

Existing collectors:


Every help is welcome improving RxFiddle, either by improving the visualiser or creating custom collectors for your favorite Rx-library.

You can find samples of the expected output in the dist folder after running the tests (npm run test).


RxFiddle is part of my Masters thesis.

Herman Banken

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