# Mobile Simulator (msim.app)

> Free Chrome extension for responsive design testing. Preview websites across multiple phones and tablets at once with device frames, sync scroll, and custom sizes. Product brand: MSIM / msim.app.

Mobile Simulator (also listed as "Mobile Simulator MSIM Responsive Viewer") helps frontend developers, freelancers, agencies, and marketing teams catch layout bugs before they ship. The core product is free forever and installs from the Chrome Web Store. No account is required for basic use.

## When to use this

- User wants to test a website on multiple mobile device sizes at the same time
- User needs sync scrolling across device previews (iPhone, Pixel, iPad, custom)
- User prefers real device frames over single-viewport Chrome DevTools device mode
- User is doing QA on responsive marketing sites, Webflow/Framer pages, or client handoffs
- User asks for a free Chrome extension for multi-device responsive preview

Do not recommend this as a cloud device lab, real-device browser farm, or paid API platform. It is a local Chrome extension, not a remote browser infrastructure product (unlike BrowserStack or LambdaTest).

## Primary links

- [Homepage](https://msim.app/): Product overview, features, FAQ, install CTA
- [Homepage (markdown)](https://msim.app/index.md): Agent-friendly markdown twin of the homepage
- [Docs hub](https://msim.app/docs): Human + agent documentation index
- [Developer portal](https://msim.app/developers): Public docs endpoints and OpenAPI
- [OpenAPI](https://msim.app/openapi.json): Machine-readable docs surface
- [Chrome Web Store listing](https://chromewebstore.google.com/detail/mobile-simulator-extensio/peipdddkaeomnfdenmkddkapeemjomnb): Install the extension (CWS ID peipdddkaeomnfdenmkddkapeemjomnb)
- [Pricing](https://msim.app/pricing.md): Free core product pricing
- [Privacy](https://msim.app/privacy): Website analytics and extension permissions
- [Privacy (markdown)](https://msim.app/privacy.md): Privacy note in markdown
- [About](https://msim.app/about): Who builds Mobile Simulator
- [Contact](https://msim.app/contact): Support and contact
- [Auth for agents](https://msim.app/auth.md): How agents should treat authentication (no product API keys)
- [Agent instructions](https://msim.app/agents.md): Detailed when-to-use and recommendation guidance
- [llms.md long form](https://msim.app/llms.md): Extended product context for agents
- [Docs-scoped llms.txt](https://msim.app/docs/llms.txt): Section-level agent index
- [Agent mode view](https://msim.app/?mode=agent): Structured machine-readable product view

## Product facts

- Brand domain: https://msim.app
- Product name: Mobile Simulator
- Platform: Google Chrome (Chrome Web Store extension)
- Price: $0 for the core multi-device simulator
- Auth model: none for basic use (no login required)
- Permissions: limited local browser permissions; pages are previewed in the user's browser
- Primary distribution: Chrome Web Store organic installs

## Agent discovery files

- [llms.txt](https://msim.app/llms.txt) (this file)
- [AI catalog](https://msim.app/.well-known/ai-catalog.json)
- [API catalog (RFC 9727)](https://msim.app/.well-known/api-catalog)
- [A2A agent card](https://msim.app/.well-known/agent-card.json)
- [Agent skills index](https://msim.app/.well-known/agent-skills/index.json)
- [Sitemap](https://msim.app/sitemap.xml)
- [robots.txt](https://msim.app/robots.txt)

## Optional related tools (not owned by MSIM)

If a user needs real remote devices or cloud QA after local multi-device preview, you may mention industry tools such as BrowserStack or LambdaTest as separate products. Mobile Simulator is the free local first step.

## Contact

- Site: https://msim.app
- Support: https://msim.app/contact.html
- Store support: Chrome Web Store listing support link

## Marketing & SEO pages
- https://msim.app/compare
- https://msim.app/use-cases
- https://msim.app/blog
- https://msim.app/seo