Code Playgrounds

20+ code playgrounds across 6+ categories. Most run entirely in your browser via WebAssembly or native browser APIs; Kotlin is the one exception, compiled on JetBrains' public service.

Programming Languages

General-purpose languages compiled to WebAssembly or running as pure JavaScript.

Python

Run Python 3 entirely in your browser - print, loops, classes, numpy.

Pyodide (WebAssembly)

JavaScript

Run modern JS - console.log, fetch, DOM APIs - in a sandboxed iframe.

Sandboxed iframe

TypeScript

Write TypeScript - type annotations are stripped, code runs as JS.

ts-blank-space + sandboxed iframe

Lua

Run Lua 5.3 scripts entirely in JavaScript - no WASM needed.

Fengari (pure-JS Lua VM)

PHP

Real PHP 8 in the browser - functions, classes, OOP, JSON.

php-wasm (PHP 8 in WebAssembly)

Real R 4.x in the browser - vectors, data frames, plots, stats.

webR (R in WebAssembly)

Perl

Perl 5 in the browser - regex, hashes, references, and the classic one-liners.

WebPerl (Perl 5 in WebAssembly)

Kotlin

Kotlin - compiled and run on JetBrains' server (the only non-browser runner).

JetBrains public compiler service

Ruby

Real CRuby 3 in the browser - blocks, classes, modules, regex.

ruby.wasm (CRuby in WebAssembly)

SQL Engines

Real SQL databases running fully in the browser - SQLite, Postgres, DuckDB.

SQLite

SQLite queries with pre-seeded tables - students, employees, orders.

sql.js (SQLite in WebAssembly)

PostgreSQL

Real Postgres in your browser via PGlite - jsonb, CTEs, window functions.

PGlite (Postgres in WebAssembly)

DuckDB

Analytic SQL in your browser - window functions, group-by, CSV reads.

duckdb-wasm

Data / Query

Pluck fields from JSON, XML and HTML with expression languages.

XPath / Selector

Test XPath and CSS selectors against any HTML / XML you paste.

Native DOMParser + document.evaluate

JSONata

Functional query language for JSON - filter, project, aggregate, transform.

jsonata

JMESPath

AWS CLI's JSON query language - paths, filters, projections, built-ins.

jmespath

Markup / Web

Live-preview HTML, Markdown and SVG straight from your source.

HTML / CSS

Live HTML + CSS preview - edit on the left, see results on the right.

Native iframe

Markdown

Write Markdown with live HTML preview - GitHub-flavoured.

remark + remark-gfm

SVG

Write SVG markup with a live render - shapes, paths, gradients.

Native iframe + SVG renderer

Diagrams / Math

Render Mermaid, KaTeX and Graphviz diagrams client-side.

Mermaid

Render flowcharts, sequence, state, class, ER and gantt diagrams from text.

mermaid.js

KaTeX (Math)

Render TeX / LaTeX maths to HTML - fast, synchronous, lightweight.

KaTeX

Graphviz / DOT

Render DOT-language graphs - directed, undirected, hierarchical, force-directed.

Viz.js (Graphviz in WebAssembly)

Logic & Functional

Declarative and functional languages - Prolog, Scheme, Clojure.

Prolog

Declarative logic programming - facts, rules, queries, backtracking.

Tau Prolog (pure JS)

Scheme / Lisp

R6RS-style Scheme interpreter - lambdas, recursion, tail calls.

BiwaScheme (pure JS)

Clojure

Real Clojure / ClojureScript in the browser - immutable data, sequences, atoms.

Scittle (browser ClojureScript)