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TraceLab

Interactive code playground

Don’t just run code. Watch it think.

Write, run, and understand code in 16 supported languages — with real output and a source-driven visual execution flow.

main.py

Python runs locally in your browser● Checking backend…

Program inputOne value per line

Input is required. Enter the value before running the program.

Output● Ready

Analyze your code to see its execution flow.

Live previewRendered in a sandboxed frame

Program flowStep 1 of 1

Start⚡

Analyze◆

Process?

Update↔

Output✓

Start — waiting for your program.

Readyline —

Start

What’s happening now

Ready. Run your program to build a source-driven trace.

Live variables

Main logic finder

TraceLab identifies functions, loops, decisions, data-structure operations, input, output and returns from your code.

Run this view on any pasted code.

16 supportedHTML / CSSPythonJavaScriptTypeScriptC / C++Java / GoKotlin / SwiftRuby / PHPPerl / BashSQL

Use ← → to move through the generated trace, or press Play flow.

How it works

TraceLab reads the structure of your source and builds a flow from the instructions it actually finds.

1

Write or paste code

Use the built-in example or paste your own program.

2

Choose a language

Pick one of the 16 supported languages or use Auto-detect.

3

Analyze & visualize

The flow is generated from your source instead of a fixed five-step story.

What actually runs

Browser languages execute locally; hosted languages use the TraceLab backend.

Live

Python

Runs in the browser with Pyodide.

Live

JavaScript

Runs in a sandboxed browser frame.

Live

HTML & CSS

Rendered in the live preview.

Hosted

12 runtimes

TypeScript, C, C++, Java, Go, Kotlin, Swift, Ruby, PHP, Perl, Bash and SQL use the TraceLab backend.

Frequently asked

Does the flow use a fixed five-step algorithm?

No. The number and meaning of timeline steps change with the source code.

Will every possible algorithm be understood perfectly?

Not yet. The frontend provides a broad source-driven trace and recognizes common DSA patterns; exact runtime tracing for every language requires backend instrumentation.

Where does hosted code run?

Hosted languages are sent to the TraceLab execution backend when you press Run.

Can I keep updating the public site?

Yes. Replace and redeploy the HTML whenever you fix bugs or add features.