CodePen vs Rust Playground

CodePen is a web-based social development environment for creating, testing, deploying, sharing and discovering front-end code. In a Pen, users write HTML, CSS and JavaScript and see a live browser preview. It supports HTML preprocessors such as Markdown, Haml, Slim and Pug, and CSS preprocessors including Sass, Less, Stylus and PostCSS. The CodePen 2.0 editor supports automatic preprocessing, live previews, file systems, version history, collaboration and one-click Pen deployment. Users can add external CSS and JavaScript resources, reuse other Pens, find libraries through CDNjs and import bare npm packages through its compiler. Pens can be embedded on other websites, and CodePen documents a REST API and other embed and prefill options. Pens and Projects are public by default. PRO users can make Pens and Collections private, but anyone with the shared URL can view them without logging in. The free plan includes unlimited public Pens and three files per Pen. Starter costs $8 a month, Developer $12 a month and Super $26 a month. CodePen does not offer a self-hosted version.

Rust Playground is a free web tool for trying Rust when a local installation or compiler is unavailable. Its syntax-highlighted editor compiles code in debug or release mode against the stable, beta, or nightly channel. The available crates include the top 100 by all-time downloads, Rust Cookbook crates, and their dependencies, though some candidates are omitted if they fail to compile on Linux or stable Rust or have invalid feature selections. Users can run rustfmt and Clippy, or inspect LLVM IR, assembly, and Rust MIR. Code can be loaded from or saved to a GitHub Gist and shared; Rust documentation and mdbook examples can also link to code for editing or execution. Docker containers supply and isolate its compilers and tools. Compilation and execution have no outside network access and are limited by memory and time. The latest entered code is saved in browser local storage, shared among windows as a single resource. The project is open source under Apache License 2.0 or MIT. Self-hosting is documented, and requires a GitHub token for Gist loading and saving.