Visualize Python, Java, JavaScript, TypeScript, Ruby, C, and C++ code execution in your Web browser
JavaScript Java HTML TypeScript Python CSS Other
Latest commit 12ad02c Feb 14, 2017 @pgbovine better error msg

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.

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/v3/

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 setups in v4-cokapi/ that I haven't yet cleanly packaged up.

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


For code or security contributions

  • John DeNero - for helping with the official Python 3 port and lots of code patches
  • Chris Horne - - for security tips
  • Joshua Landau - - for security tips
  • David Wyde - - for security tips
  • Peter Wentworth and his students - for working on the original Python 3 fork circa 2010/2011
  • Brad Miller - for adding pop-up question dialogs to visualizations, and other bug fixes
  • David Pritchard and Will Gwozdz - for the Java visualizer and other frontend enhancements
  • Peter Robinson - for v3/
  • Chris Meyers - for custom visualizations such as v3/ and v3/
  • Irene Chen - for holistic visualization mode -- v3/js/holistic.js

For general advice and feedback about this project:

  • Ned Batchelder
  • Jennifer Campbell
  • John Dalbey
  • John DeNero
  • Fredo Durand
  • Michael Ernst
  • David Evans
  • Paul Gries
  • Mark Guzdial
  • Adam Hartz
  • Sean Lip
  • 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!