UCSD - University of California - San Diego

03/19/2026 | Press release | Distributed by Public on 03/19/2026 03:15

A UC San Diego Tool Teaching Code to 25 Million is Even More Critical in Age of AI

Published Date

March 19, 2026

Article Content

Key Takeaways

  • UC San Diego cognitive scientist Philip Guo created Python Tutor, a free tool that makes code "visible" step by step.
  • The research behind it earned a Test of Time award, recognizing its enduring influence over the past 15 years.
  • Python Tutor has reached 25M+ learners in 180+ countries, with 500M+ visualizations and 10k-20k daily users.
  • In the age of AI, coding literacy matters more: people must evaluate and debug AI-generated code that can be wrong.

When generative AI began writing code with uncanny fluency, it sparked a major question: If a chatbot can build software, do people still need to learn how to code?

UC San Diego Professor of Cognitive Science Philip Guodoesn't hesitate. In fact, he argues that understanding code is now more important than ever - a view underscored by a recent "Test of Time" award he received, which recognizes research in coding education published years prior that had a lasting, significant impact on the field.

"AI may generate code faster than any human," Guo said. "But the need to understand what code is doing has only intensified. AI generates code that may seem right, but it isn't always reliable. You need to evaluate, debug and steer the code that AI produces."

That need is at the heart of Python Tutor, a free online platform created by Guo that visualizes code execution step by step-turning a famously invisible process into something learners can actually see. The tool's reach is vast - among the largest for any educational project created in a university lab. First established in 2010, Python Tutor has reached 25+ million users across 180+ countries. It has created more than 500 million code visualizations, and has about 10,000 to 20,000 people using it daily. Teachers from tens of thousands of universities and K-12 schools around the world have used it during class to help students understand their code. And millions of learners of all ages have used it while taking online courses such as those from Coursera, edX and Udemy.

Making the invisible visible

Programming is difficult for beginners for a simple reason: the computer's logic isn't naturally observable. Guo describes this as a "foundational challenge" - people must form accurate mental models of what happens as a computer runs code step-by-step, even though what's going on behind the screen is invisible.

Python Tutor tackles this problem head on - instead of asking learners to guess what's happening under the hood, it shows them - line by line - what variables and data structures look like in code. It walks them through, step by step, how the information in the program changes and how one step leads to the next as the computer runs it. It's a deceptively simple idea with outsized impact, powering learning for beginners in Python and other commonly used programming languages such as Java, C, C++, and JavaScript.

Why Python Tutor matters more now than ever

At first glance, AI code generators like ChatGPT, Claude, and Gemini might seem like a shortcut past the struggle of learning to program. But Guo's perspective is the opposite: AI expands what people can build - but also raises the stakes for understanding how coding works.

"One of the areas where AI has done the best so far is coding," Guo said. "That means more people can attempt software creation, including people across fields ranging from the social sciences, to business and the humanities, but critically, they still need to learn something about how programming works on a fundamental level. Otherwise it is impossible for someone who has no idea about software or code to just talk to AI and build something that is safe and reliable."

In other words: AI can produce code output, but people still need the literacy to steer it, evaluate it, and fix it when it breaks. And visualization tools like Python Tutor, coupled with carefully-designed lessons, can help novices develop this kind of foundational coding literacy.

Credit: Philip Guo
UC San Diego Professor of Cognitive Science Philip Guo. Credit: UC San Diego.

A tool for learning - and for the workforce

Guo's tool also lowers the barrier for learners who don't fit the traditional "computer science major" pipeline - career changers, students in non-STEM fields and professionals who need to become conversant in software to collaborate effectively in multidisciplinary teams.

Guo connects this to a new category he and collaborators identified in earlier research: "conversational programmers," people who learn enough programming to communicate and work better with software engineers. In the AI era, he believes the idea has evolved: those learners aren't only conversing with human engineers anymore - they're increasingly "in conversation with AI tools," using programming fundamentals to make AI-generated software usable in the real world.

Guo first published on the idea of conversational programmers in a 2015 paper, co-authored with Parmit Chilanaat Simon Fraser University, which also received a "Test of Time" award alongside the long-term impact award for Python Tutor.

An AI tutor, built on research

Python Tutor itself has evolved to the moment - recognizing that learners today are increasingly relying on AI as a virtual tutor. Guo created a built-in AI chat feature that can guide learners through visualized code execution - explaining the diagrams as an expert teacher would. It's an important distinction: the goal isn't just to hand learners an answer, but to help them build a deep understanding of fundamentals - so they can debug, verify, and reason about future AI-generated code rather than accept it without question.

Behind Every Breakthrough: research funding makes public impact possible

Python Tutor's incredible growth in impact over the past 15 years may mirror a tech startup success story. But Guo is clear that he doesn't want it to become a corporate product. It's designed to remain free, accessible and not-for-profit, serving teachers and learners around the world.

That mission depends on continual research support. Guo emphasizes that keeping the platform - and its AI features - free has been possible because it's supported through federal research dollars from organizations such as the U.S. National Science Foundation, which awarded Guo a CAREER grant. That investment enables ongoing development, maintenance and student involvement - turning research into a public resource used by tens of millions around the world.

"This work shows that research funding doesn't just advance knowledge," Guo said. "Sometimes, it enables the construction of a tool that quietly becomes part of the global infrastructure for learning."

AI may be transforming how software gets written. But Guo believes the timeless skill underneath - understanding how logic works, step by step - still matters. And for millions of learners worldwide, Python Tutoris where that understanding begins.

Learn more about research and education at UC San Diego in: Artificial Intelligence

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