Best Online Python Compilers Compared

The best online Python compiler depends on what you need to do. A browser-based runtime such as WebFiddle or Brython keeps code on your device, a simple server-backed editor like Programiz is quick for exercises, Google Colab suits notebooks and machine learning, and Replit is aimed at building and publishing full apps. This comparison sets out how each one works so you can choose for yourself.

Key takeaways#

• "Online Python compiler" covers two different designs: code that runs in your browser (WebFiddle, Brython) and code that runs on a remote machine (Colab, Replit).
• Browser-based runtimes keep code on your device and need no account, but they're limited by the browser sandbox.
• Cloud tools can offer full Linux environments, GPUs or hosting, but your code runs on someone else's computer and usually requires an account.
• WebFiddle runs CPython 3.12 through Pyodide 0.26.1. Pyodide can load packages like NumPy and pandas, but the sandbox doesn't preload them.

Disclosure: WebFiddle is our own product. We've tried to describe every tool, including ours, using only facts from each project's own website or documentation, and we don't rank the tools.

How we compared them#

We looked at factual attributes you can check yourself:

1. Where code runs: in your browser or on a remote server.
2. Python implementation: CPython or another implementation.
3. Packages: whether you can use third-party libraries.
4. Account: whether you need to sign in to run code.
5. Best fit: the use case each tool is designed for, based on how the tool describes itself.

We don't include speed rankings, because performance varies with your device, network and workload.

Comparison table#

WebFiddle#

How it works: the WebFiddle Python sandbox loads Pyodide 0.26.1, a port of CPython 3.12 to WebAssembly, into a Web Worker. Your code runs on your own device, and output is streamed back to the page.

Strengths:

• Runs locally: the code you run isn't sent to an execution server.
• No account: open the page and run code.
• Real CPython: standard-library behaviour matches Python 3.12.

Limitations:

• First load: the browser has to download the Pyodide runtime before the first run.
• Packages aren't preloaded: NumPy, pandas and matplotlib are in Pyodide's package list, but the sandbox doesn't load them automatically, so import numpy fails until you load the package. Pyodide's package loading guide covers the options: pyodide.loadPackage() for packages built for Pyodide, and micropip for pure-Python wheels from PyPI.
• Browser sandbox: there is no access to your computer's files, no raw sockets and no subprocesses.
• Text output: the sandbox shows standard output and errors. Plots and GUI windows aren't displayed.

Programiz#

How it works: the Programiz online Python compiler is a single-file editor with Run and Share buttons, placed next to Programiz's Python tutorials. The page doesn't state where code is executed or which packages are available.

Strengths: a minimal interface that suits students working through tutorial exercises.

Limitations: it's built for short programs rather than projects, and the page doesn't document package or environment details.

Google Colab#

How it works: according to the Colab FAQ, Colab is based on Jupyter notebooks, and "code is executed in a virtual machine private to your account". It is free of charge to use.

Strengths:

• Notebooks: mix code, output, charts and Markdown notes in one document.
• Accelerators: GPUs and TPUs may be available. The FAQ says the available types vary over time and "resources are not guaranteed and not unlimited".
• Packages: you can install libraries into the VM.

Limitations: you need a Google account, and idle virtual machines are deleted, with a maximum runtime enforced by the service. It isn't designed for hosting web apps or long-running bots.

Replit#

How it works: Replit is a cloud platform for building apps. Its documentation describes chat, build and design tools for turning ideas into apps and sites and publishing them.

Strengths: full projects with multiple files, packages and publishing in one place.

Limitations: code runs in the cloud and requires an account. Replit's pricing page lists paid Core, Pro and Enterprise plans, so check current plan limits before relying on it for a class.

Brython#

How it works: Brython describes itself as "a Python 3 implementation for client-side web programming". It runs in the browser with an interface to the page's DOM, so you can handle web page elements and events in Python:

from browser import document

document["my-button"].text = "Clicked!"

This snippet needs Brython on a web page that has an element with the id my-button. It won't run in a regular Python interpreter.

Strengths: it's designed for writing front-end code in Python.

Limitations: Brython is its own implementation of Python rather than CPython, so C-extension packages such as NumPy aren't available.

Which should you choose?#

• Trying out a snippet or learning syntax without signing in: a browser runtime such as WebFiddle.
• Working through beginner exercises from a tutorial site: Programiz.
• Data analysis or machine learning in notebooks: Google Colab.
• Building and publishing a full app: Replit.
• Manipulating a web page with Python: Brython.

Once you've picked a tool, practise with our guide to Python list comprehensions with examples, or read whether WebAssembly is the future of web development to understand how browser runtimes like Pyodide work.

Frequently asked questions#

Which online Python compiler runs code without sending it to a server?

Browser-based runtimes run code on your own device. WebFiddle uses Pyodide, which is CPython compiled to WebAssembly, and Brython implements Python on top of JavaScript. Both execute inside the browser tab. Google Colab and Replit execute code on remote machines, so your code and data are sent to their cloud infrastructure.

Can I use NumPy and pandas in the WebFiddle Python sandbox?

NumPy and pandas are available as Pyodide packages, but the WebFiddle sandbox doesn't preload them, so a plain import fails at first. They must be loaded through Pyodide's package loader before importing. Pure-Python libraries from PyPI can be installed with micropip. Packages that need native code not built for Pyodide won't work.

What Python version does WebFiddle use?

The WebFiddle Python sandbox runs Pyodide 0.26.1, which is built on CPython 3.12. Language features and standard library behaviour therefore match Python 3.12, including f-strings, pattern matching and the other features that release introduced. Features that need operating system access, such as subprocesses, threads or raw network sockets, are limited by the browser sandbox.

Is Google Colab free?

Google's Colab FAQ says Colab is free of charge to use. Free resources such as GPUs are not guaranteed, their types vary over time and usage limits can fluctuate, and idle virtual machines are shut down. Paid plans offer more compute. You need a Google account to run notebooks.

Why is WebFiddle included in this comparison?

WebFiddle is our own product, and we've disclosed that at the top of this article. We included it because it's a browser-based Python runtime. We don't rank it above the other tools. Instead, we describe how each one works using publicly documented facts, so you can choose based on your needs.