To capture a localhost site in a cloud browser, first start a tunnel from your computer to TestMu AI’s browser-testing cloud, then open your local site through that tunnel and capture it in the browser and viewport you want. TestMu AI is the current name for LambdaTest; older guides and interface references may still use LambdaTest terminology.
Why a tunnel is needed
A cloud browser normally cannot reach a web server running on your computer’s private localhost address. The tunnel creates an encrypted connection from your machine to the vendor’s cloud browsers, so a remote test session can access the locally hosted page. TestMu AI’s documentation describes TCP with TLS 1.2 over port 443 and WebSocket over port 443; its tunnel binary scans the network and selects a mode unless you explicitly choose one. See the official locally hosted pages documentation.
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Before you start
- Run your development server and confirm the page loads in a browser on the same machine. The server command depends on your framework; use the command for your project and note the local port.
- Have access to a TestMu AI account and the local testing or screenshot workflow you intend to use.
- Allow the tunnel application to make outbound connections to the vendor’s servers over port 443.
- Keep your access key and API token private. TestMu AI identifies them as confidential credentials: do not put them in public code, repositories, or exposed environments. If credentials are compromised, revoke and regenerate them.
Start a tunnel and capture the page
- Start your local site. Verify the exact page and port locally before opening a cloud session. A running tunnel cannot fix a stopped development server or a route that does not work on your machine.
- Choose a tunnel setup. Download and run the binary matching your operating system and machine architecture, following the current instructions in TestMu AI’s support documentation. Alternatively, use UnderPass, the graphical application TestMu AI describes as a way to set up the tunnel without terminal commands. The product page also lists an npm plugin and GitHub Actions integration for local testing; their availability and setup details may depend on the current product workflow.
- Authenticate and start the tunnel. Follow the instructions for your account and selected setup method. Do not paste a real key into a public example, shared terminal transcript, or repository. Unless you explicitly configure a mode, the binary selects a connection mode after scanning the network.
- Open the local page in the cloud session. Use the local address and port in the format recognized by the tunnel configuration. Do not assume the remote browser’s literal
localhostis automatically your computer’s localhost: use the current tunnel instructions for any host alias, port mapping, or URL transformation required. - Choose a browser and viewport, then capture. Use the local-browser-testing or screenshot-testing workflow available in your account. For cross-browser checks, select the browsers you need; for responsive checks, use the intended viewport or device combinations. The vendor’s screenshot feature article says desktop-resolution selection applies to desktop devices and directs mobile checks toward responsive testing. Interface labels and entitlements can change, so confirm them in the current product UI.
- Review or share the result. The vendor describes shareable results, saved test configurations, and support for screenshots of pages behind login. Follow the current workflow and verify account or plan availability before relying on a particular control.
- Stop the tunnel when finished. Close the binary or UnderPass session using its current instructions. If you exposed a credential, revoke it and generate a replacement.
Choose the right setup and coverage
| Choice | Use it when | What to keep in mind |
|---|---|---|
| Command-line tunnel binary | You prefer terminal-based setup or need to fit tunnel startup into an automated workflow. | Choose a binary for the machine’s operating system and architecture, and follow the current vendor instructions. |
| UnderPass graphical app | You want a desktop setup described by the vendor as avoiding terminal commands. | Follow the current app workflow; older LambdaTest guides may show different names or screens. |
| One-off manual screenshot | You need to inspect a page in a particular browser or viewport. | Start the tunnel and select the relevant configuration in the current testing workflow. |
| Repeated or matrix screenshot testing | You need screenshots across selected browser or device combinations. | The vendor describes automated screenshot testing and configuration choices; exact availability may depend on the current account and packaging. |
| Desktop viewport | You are checking desktop layouts at chosen resolutions. | The vendor says its desktop-resolution selection applies to desktop devices. |
| Mobile device coverage | You are checking mobile rendering and responsive layouts. | The vendor points to responsive testing for mobile device combinations. |
Published tunnel requirements
TestMu AI’s support documentation, marked as last updated September 11, 2026, lists these requirements. They are the vendor’s published minimums, not independent performance measurements:
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- x86_64 or ARM64 architecture.
- At least one physical CPU core, 2 GB RAM, and 200 MB of disk space.
- Permission to execute the tunnel binary and outbound access to vendor servers over port 443.
Troubleshooting
The cloud browser cannot open the page
- Confirm the local server is running and the same page loads on your machine.
- Check the port and route. The cloud session needs the address and port recognized by the tunnel, not an assumed mapping.
- Make sure the tunnel is running and authenticated, and that outbound connections over port 443 are permitted.
- Consult the current tunnel instructions for the required local host alias or URL format; a remote browser’s own
localhostmay not mean your development machine.
The tunnel will not start or connect
- Check that you downloaded a binary for your operating system and architecture and have permission to execute it.
- Verify the machine meets the vendor’s published requirements and can make outbound connections to the vendor over port 443.
- If network scanning does not select a usable mode, follow the official instructions for explicitly setting one.
- Recheck credentials without sharing them. If they may have been exposed, revoke and regenerate them.
The screenshot differs from the expected layout
- Check that you selected the intended browser and viewport or device type; desktop resolution controls are not a substitute for mobile responsive testing.
- Confirm the page is fully available locally, including any route that requires authentication. The vendor describes behind-login screenshot support, but use the current workflow and account entitlements.
- Allow the page’s content and assets to load before capturing, then inspect the result in the same browser/device configuration.
Or skip the browser setup: use ScreenshotNeo
If you only need a screenshot of a publicly reachable page and do not need to inspect it in a live cloud browser, ScreenshotNeo offers a one-request alternative. It is a website screenshot API and MCP server from Yorker Media. See ScreenshotNeo and its API documentation.
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curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpReplace the example URL with the page you want to capture. ScreenshotNeo also accepts the parameter names used by other screenshot APIs. It removes cookie/consent banners, newsletter popups, and chat widgets before capture; each cleanup step can be turned off. Bot checks, blank pages, failed loads, timeouts, and cache hits are not billed, and responses identify the page verdict and billing status in headers. Its MCP server provides take_screenshot, get_page_info, and capture_pdf tools for AI agents and other MCP clients.
The free plan includes 1,000 screenshots per month with no card; paid plans start at $5 for 3,000 screenshots, and yearly billing gives two months free. Sign up for ScreenshotNeo’s free plan.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When to use each approach
Use TestMu AI when the task depends on checking the local site in a real cloud browser, comparing browser/device configurations, or working through its screenshot-testing workflow. Use ScreenshotNeo when an API request or MCP tool is a better fit for capturing a page without setting up that browser session. An API screenshot does not replace interactive cross-browser testing of a private localhost site.
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