Validate the system, not a single artboard
Check spacing, type scale, and component behavior across real viewport widths before the build drifts.
- Side-by-side breakpoint proof
- Client-ready device frames
- Catch clip & overflow early
MSIM Mobile Simulator
Free · Chrome & Firefox · Design · PM · QA
See every screen at once.
Ship layouts that survive reality.
Side-by-side device previews with sync scroll — so designers, PMs, and testers catch responsive bugs before users do.
Built for the people who own the UI story — not just the CSS.
Designers
Product managers
Testers / QA
Product demo
See MSIM in action
A real walkthrough of multi-device preview, sync scroll, and the daily responsive workflow.
Social proof
Already in daily responsive workflows
Chrome Web Store metrics. Free core product — no account required.
3,240+
Downloads
1.5k+
Weekly active users
5.0
Chrome Web Store rating
$0
Core product price
“I stop guessing breakpoints. Open three devices, sync scroll once, and the overflow is obvious before handoff.”
“Great for PR and stakeholder checks: phone + tablet + wide phone on the real staging URL, no deck of screenshots.”
“QA passes go faster when frames look like real devices and sync scroll keeps every viewport aligned.”
Who it’s for
One board. Three jobs done faster.
MSIM sits between Figma and production — where layout truth gets verified.
See the product story on every screen
Review flows on phone and tablet without waiting for a screenshot pack or a DevTools walkthrough.
- Instant multi-device walkthroughs
- Staging & logged-in sessions
- Clearer go / no-go calls
Regression passes without viewport hopping
Run checklist items across presets in one view — sync scroll makes layout diffs jump out.
- Faster responsive smoke tests
- Custom sizes for edge cases
- Rotate & refresh in one click
Stop hopping one viewport at a time.
Browser support
Available on Chrome and Firefox
Install Mobile Simulator from the official Chrome Web Store or Firefox Add-ons. Same multi-device preview workflow in the browser you already use.
Google Chrome
Install from the Chrome Web Store. Works on Chromium-based browsers that support Chrome extensions.
Get it for ChromeMozilla Firefox
Install from Firefox Add-ons. Built for the same responsive QA workflow inside Firefox.
Get it for FirefoxFeatures overview
Responsive truth, without the ritual
Built for design reviews, PM walkthroughs, and QA checklists — fewer DevTools switches, clearer multi-device overview.
Design
- Multi-device view
- Real device frames
- Modern presets (iPhone, Pixel, Galaxy, iPad)
Product
- Sync scrolling
- Quick action packs
- Staging & localhost friendly
QA
- Custom viewports
- One-click rotate & refresh
- Breakpoint validation before ship
Multi-device preview
Open iPhone, Android, and tablet sizes side by side — no dragging the browser window around.
Sync scrolling
Scroll once, watch every device move together so layout bugs jump out immediately.
Device frames
Toggle realistic frames for stakeholder-ready previews, or turn them off for pure layout work.
Custom sizes
Add any width and height when presets are not enough for your breakpoint system.
Quick action packs
Jump into mobile-only, tablet-only, popular 3-pack, or iOS/Android sets in one click.
Rotate & refresh
Flip orientation and reload all views from the toolbar while you iterate on the UI.
Differentiation
Works on the real site in your browser tab
MSIM is not a cloud device farm. It previews the page you already opened — local, staging, and logged-in sessions stay in context.
Localhost & staging
Open localhost or staging in Chrome, launch MSIM, and compare devices without uploading a build to a remote lab.
Authenticated apps
If you are already signed in on the tab, the simulator runs on that same session. No separate login sandbox required for basic preview.
Real multi-device overview
Side-by-side phones and tablets with optional frames beat resizing one DevTools viewport over and over.
Honest limits
Some sites block embedding with security headers. MSIM surfaces that clearly. We optimize for real developer tabs, not unlimited fake iframes.
Many generic responsive viewers struggle with localhost, staging, authenticated apps, and iframe restrictions. MSIM focuses on the browser-tab workflows design, product, and QA teams already use.
Why not only Chrome DevTools?
DevTools is one viewport. MSIM is a multi-device board.
Keep DevTools for DOM inspection. Use MSIM when you need speed and visual comparison across breakpoints.
| Chrome DevTools | MSIM |
|---|---|
| One device at a time | Multiple devices side-by-side |
| Manual switching between sizes | Immediate comparison board |
| Slower visual overview | Faster validation with sync scroll |
| Great for DOM debugging | Great for design QA, PM reviews & layout passes |
How it works
Three steps. Zero setup drama.
Install once. Use it on any tab. No account, no config files.
-
1
Add the extension
Install from the Chrome Web Store or Firefox Add-ons in seconds. Lightweight permissions only.
-
2
Open any website
Click the extension, pick devices from the library, hit Open Selected.
-
3
Compare and fix
Use sync scroll, rotate, and multi-device view to catch layout issues before clients do.
Use cases
Fits design, product, and QA rituals
From design handoff to release checklist — multi-device proof without the ceremony.
Responsive development
Check layouts across devices before you open a PR or tag a release.
Read use case →QA testing
Catch breakpoint issues quickly without reconfiguring DevTools for every size.
Read use case →Agency workflow
Validate client sites across devices and share clearer visual checks with stakeholders.
Read use case →E-commerce optimization
Verify mobile shopping layouts, product grids, and checkout breakpoints faster.
Read use case →Web designers
Product managers
Testers & QA
Frontend & agencies
FAQ
Questions, straight answers
Is Mobile Simulator free?
Yes. The core multi-device simulator is free forever. No account required for basic use.
How is this different from Chrome DevTools device mode?
DevTools is great for one viewport. Mobile Simulator is built for comparing multiple real device sizes at once with frames, sync scroll, and quick presets.
Will it reorganize the UI I already know?
No. We polish devices and quality, but keep the same Devices / Settings / Quick Actions flow so existing users do not relearn anything.
Why do some sites not load inside the simulator?
Some websites block embedding with security headers. When that happens, the tool shows a clear message. We keep improving reliability without bloating permissions.
Do you show ads?
No display ad networks inside your pages. The core simulator stays free. We may later show optional, disclosed partner tool suggestions. None are live on this site yet.
Which browsers are supported?
Mobile Simulator is available for Google Chrome and Mozilla Firefox.
Where do I get support?
Email support@msim.app, use the contact page, or the support link on the Chrome Web Store / Firefox Add-ons listing.
Install free. Review every screen. Ship cleaner UI.
Multi-device responsive checks for designers, PMs, and testers — in Chrome or Firefox.