Visualize Python, Java, JavaScript, TypeScript, Ruby, C, and C++ code execution in your Web browser
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Python Tutor -- -- helps people overcome a fundamental barrier to learning programming: understanding what happens as the computer executes each line of a program's source code. Using this tool, you can write Python, Java, JavaScript, TypeScript, Ruby, C, and C++ programs in your Web browser and visualize what the computer is doing step-by-step as it executes those programs.

This tool was created by Philip Guo in January 2010. See project history.

The latest development version of the code is in v5-unity, although lots of legacy documentation still resides in v3.

All documentation is viewable online at:

Quick Start

BY FAR the most preferred way to use Python Tutor is via the official website, since it contains the latest updates:

You can use iframe embedding to easily embed visualizations on your webpage.

If you want to run locally on your own computer, to run Python visualizations try:

pip install bottle # make sure the bottle webserver ( is installed
cd OnlinePythonTutor/v5-unity/

You should see the visualizer at: http://localhost:8003/visualize.html

... and the live programming environment at: http://localhost:8003/live.html

However, it can be hard to run your own visualizer locally for non-Python languages, since there are complex dependencies in v4-cokapi/ that I haven't yet cleanly packaged up. By default, the local version you run will call my own server to run the non-Python backends, so please be mindful of your bandwidth usage.

For further directions, see Overview for Developers or explore the rest of the docs.


For code or security contributions:

  • Irene Chen - experimental holistic visualization mode - v3/js/holistic.js
  • John DeNero - helping with the official Python 3 port, bug fixes galore
  • Mark Liffiton - localStorage bug fix
  • Chris Meyers - custom visualizations such as v3/ and v3/
  • Brad Miller - adding pop-up question dialogs to visualizations, other bug fixes
  • David Pritchard and Will Gwozdz - Java visualizer and other frontend enhancements
  • Peter Robinson - v3/
  • Peter Wentworth and his students - working on the original Python 3 fork circa 2010-2011
  • Security tips and vulnerability reports: Aaron E. (, Chris Horne (, Joshua Landau (, David Wyde (

For user testing and feedback from instructors' perspectives:

  • Ned Batchelder
  • Jennifer Campbell
  • John Dalbey
  • John DeNero
  • Fredo Durand
  • Michael Ernst
  • David Evans
  • Paul Gries
  • Mark Guzdial
  • Adam Hartz
  • Sean Lip
  • Fernando Perez
  • Tomas Lozano-Perez
  • Bertram Ludaescher
  • Brad Miller
  • Rob Miller
  • Peter Norvig
  • Andrew Petersen
  • David Pritchard
  • Suzanne Rivoire
  • Guido van Rossum
  • Peter Wentworth
  • David Wilkins

... and many, many more!