Test Breakpoints.
Near-Instant.
Near-Instant.
Near-Instant.
The ultimate online responsive design tester. Write CSS media queries and instantly toggle between mobile, tablet, and desktop views without ever leaving the IDE.
Pixel-Perfect Responsive Debugging.
Stop dragging your browser window back and forth. Simulate mobile, tablet, and desktop viewports simultaneously to debug complex CSS media queries with absolute precision.
Live Viewport Emulation
Toggle between standard breakpoints instantly. Our isolated iframe environment ensures your CSS behaves exactly as it would on real hardware, without interference from the editor UI.
@media (max-width: 768px) {
.grid { grid-template-columns: 1fr; }
}
Fluid Resize Controls
Identify layout breaks by smoothly dragging the viewport width. Pinpoint the exact pixel where your typography or flexbox layout starts to fail.
📱 iPhone 14 Pro Layout
Hot Module Reloading
Tweak your media query variables in the CSS panel and watch the emulated viewport update without a page refresh. Unmatched speed for UI polishing.
body { background: var(--bg); }
Full Workspace. $0.
Other cloud web IDEs charge you monthly just to keep your frontend projects private. We built a free, local code editor for the community.
Free Forever — The Only Plan
Every built-in feature free. No card required.
How It Works
Four steps to a layout that holds at every width.
Step 1 — Write your CSS
Author your styles and media queries in the CSS panel of the Monaco editor, with autocomplete for properties and values as you go.
Step 2 — Pick a viewport
Jump between mobile, tablet, and desktop presets to see how each breakpoint behaves — no more dragging your actual browser window back and forth.
Step 3 — Drag to find the break
Drag the viewport edge fluidly and watch the live width readout. You'll spot the exact pixel where a grid collapses or type starts to overflow.
Step 4 — Iterate without refreshing
Tweak a media query and the emulated viewport updates instantly through hot module replacement. Fix, drag, verify — in seconds.
Common Questions
Straight answers about responsive testing.
Which viewports can I simulate?
Standard mobile, tablet, and desktop presets cover the common breakpoints, and the fluid resize handle lets you test any width in between — including the awkward in-between sizes where layouts usually break.
Does the emulated preview behave like a real device?
Your page runs in an isolated iframe, so media queries and viewport units respond exactly as they would in a real browser window — with none of the editor's own UI interfering with measurements.
Can I test Tailwind's responsive prefixes here?
Yes. Write classes like md:grid-cols-2 or lg:px-8 and toggle the viewport emulator to watch each breakpoint kick in live.
Do I have to refresh after changing my CSS?
No. Hot module replacement pushes style changes into the preview the moment you type, at whatever viewport width you're currently testing.
Is my design work private?
Completely. Everything — your code, the preview, the viewport tests — runs locally in your browser. Nothing is uploaded to NitroIDE, and there is no code telemetry — site analytics is GA4 only.