Three focused editors
Dedicated HTML, CSS and JavaScript panes with Monaco completion, validation and hover information.
Free · local-first · no account
A web playground that stays out of your way.
Plainpen is a focused online HTML, CSS and JavaScript playground. Write browser code, see the result instantly and send the whole experiment as a compressed link.
Everything you need
Plainpen keeps the original promise of a web code playground: open it, write standard browser code, see what happens and share the result. There are no projects, feeds, teams or build pipelines to manage.
Instant live result
A native sandboxed iframe runs the browser code directly, with automatic or manual updates.
Responsive preview
Test fluid output or scale fixed 16:9, 4:3, square and phone viewports into the available pane.
Console capture
Inspect logs, warnings and runtime errors without leaving the workspace.
Local by default
Your current pen is saved in your own browser. Plainpen has no account database or save API.
Shareable by URL
HTML, CSS, JavaScript and workspace settings are compressed into a versioned URL fragment.
How it works
No virtual machine, container, package manager or server-side execution sits between the source and the browser. Plainpen builds a small document and runs it inside an isolated preview.
HTML + CSS + JS
browser document
sandboxed iframe
live result
Private by design
Ordinary pens never leave the browser. A share link contains the compressed source, and its URL fragment is interpreted by the receiving copy of Plainpen rather than stored in an application database.
Deliberately limited
Plainpen is for standard HTML, CSS and JavaScript experiments. It intentionally does not install npm packages, run framework build systems or turn a quick idea into a project-management surface.