Cross-browser testing gets faster by running independent tests at the same time across the browser engines, versions, operating systems, and devices you choose. The speed comes from parallel workers or remote sessions—not from eliminating browser coverage. “Ultrafast” also names Applitools’ visual-testing workflow, which renders captured page data in parallel; that is a specific product approach, not how every cross-browser test grid works.
How parallel cross-browser testing works
- Choose targets. Select the browser engines, versions, operating systems, viewport sizes, and devices that matter for your users and compatibility risks. Playwright, for example, lets you define browser projects, with Chromium, Firefox, and WebKit among its default examples. Playwright browser documentation.
- Write or reuse tests. A functional test can load a page, enter information, submit a form, and assert the expected result. Where the tool supports it, run compatible tests against multiple browser targets. SmartBear documents a workflow that records a web test locally, removes local-browser-specific operations, then uses XPath or CSS selectors to find elements in remote browsers. SmartBear’s parallel testing documentation.
- Distribute independent work. Run separate tests or browser projects concurrently on local workers, a private Selenium Grid, or a hosted browser service. A hosted grid provisions remote sessions; a self-managed grid gives the team responsibility for its own infrastructure. BrowserStack describes parallel runs on its hosted grid, while SmartBear documents assigning supported tests to remote environments. BrowserStack Automate.
- Collect and assess results. Functional assertions indicate whether interactions and expected outcomes passed. Visual tests compare rendered screens with baselines and flag differences for review. Tools may aggregate results, logs, screenshots, or visual comparisons differently; confirm which diagnostics are available before choosing a workflow.
- Triage and adjust capacity. Separate application defects from browser-specific behavior, test incompatibilities, and infrastructure failures. More concurrency helps only while compatible tests and available workers, licenses, remote sessions, and machine resources allow additional work to run.
Parallelism reduces elapsed time when there is enough independent work to distribute. It does not choose the right coverage for you, make incompatible tests parallelizable, or guarantee that each run is faster if infrastructure becomes the bottleneck. SmartBear documents resource and test-category constraints.
What “Ultrafast” means
In ordinary usage, “ultrafast cross-browser testing” can mean parallel testing across browsers. In Applitools product material, Ultrafast refers to a named visual-testing workflow: tests capture DOM and CSS data, the data is rendered in parallel on the Ultrafast Grid, and Applitools Eyes performs visual analysis. Applitools’ 2022 e-book says Eyes uses data captured by the first test to re-render screens, rather than separately connecting to and loading the application in each cloud environment. These are Applitools’ descriptions of its own method, not a universal definition of browser testing. Applitools Ultrafast Test Cloud e-book Applitools report.
A different common model executes automation in each selected browser environment. Playwright projects define browser targets, and hosted testing services provision remote browser or device sessions. Choose based on what you need to verify: running interactions in actual browser sessions and comparing visual renderings answer related, but not identical, questions. Playwright browser projects BrowserStack Automate.
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Choose a testing setup by its trade-offs
| Approach | What runs | Useful when | What to check |
|---|---|---|---|
| Local browser projects | Automation runs against browser engines configured on the team’s machines or CI workers. | You want a directly configured set of browser targets and control over local execution. | Installed browser availability, machine capacity, and whether the selected targets represent the environments that matter to your users. Playwright |
| Private Selenium Grid | Tests are distributed among browser nodes managed by your team. | You need control over grid infrastructure or access to environments your team provisions. | Grid setup, node capacity, maintenance, and whether your test framework and test types are supported. |
| Hosted browser/device grid | A provider runs tests in remote browser or device sessions. | You want access to remote environments without managing all browser infrastructure yourself. | Available combinations, account concurrency limits, secure access to development apps, session capacity, and diagnostics. BrowserStack advertises 3,000+ desktop and mobile browser combinations and hundreds of parallel tests; these are vendor claims, so verify current availability and limits for your account. BrowserStack Automate |
| Captured-page visual rendering | Captured page data is rendered in parallel for visual comparison, as described for Applitools Ultrafast Grid. | You want visual analysis across rendered variants and the chosen workflow supports your app and test needs. | How the tool captures page state, which visual differences it reports, baseline review, and whether this meets your need to execute functional interactions in each target browser. Applitools Ultrafast Test Cloud e-book |
Plan browser coverage and concurrency
Select a useful target matrix
- Start with browser engines and environments used by your audience, then add targets tied to known compatibility risks. A list of supported targets is not automatically a sensible test matrix.
- Decide whether you need desktop browsers, mobile browsers, real devices, or particular viewport sizes. Verify that the chosen framework or service supplies those targets.
- Use browser projects or remote environment settings to make the selected targets explicit and repeatable. Review the target list when your audience, app, or supported browser versions change.
Estimate the value of more workers
More workers can reduce the wait when there are enough independent tests, but usable concurrency is bounded by test compatibility, local CPU and memory, service session limits, licenses, and grid capacity. A large worker setting cannot make a single long test divide into independent work; it can also add contention or queueing. Increase concurrency in measured increments and check both elapsed time and failure patterns.
SmartBear notes that its parallel mode has test-type restrictions, including image-based tests and certain desktop and local-browser test types. Check the current documentation for your product and version rather than assuming every test can be distributed. SmartBear parallel testing restrictions.
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What performance claims can—and cannot—tell you
Applitools’ 2020 report describes a study involving 203 Selenium, Cypress, and Webdriver.IO engineers and 3,112 combined hours spent writing, running, analyzing, reporting, and maintaining 21 cross-environment tests. In that report, Applitools claims an 18x faster full test cycle, 81x greater code efficiency, and a 77% increase in engineer satisfaction. These are vendor-reported results from that study, not a general performance guarantee or an independent comparison of all testing approaches. A team’s outcome depends on its suite, baseline workflow, targets, and available capacity. Applitools 2020 report.
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Common troubleshooting checks
A test passes locally but fails on a remote browser
- Check for local-browser-specific operations, selectors that rely on unstable page structure, and differences in viewport or browser behavior.
- Confirm the remote environment actually matches the browser, operating system, and device you intended to test.
- Use the remote run’s logs and screenshots, where available, to distinguish an application failure from session or environment setup problems.
Parallel runs do not finish much sooner
- Check whether tests are genuinely independent and eligible to run concurrently.
- Compare the configured worker count with available machine resources, grid nodes, service session limits, and licenses.
- Look for queueing or resource contention before increasing concurrency again.
Some tests are missing from a parallel run
Check the tool’s supported test categories and project-specific restrictions. SmartBear, for example, documents limits on certain image-based, desktop, and local-browser tests in its parallel mode. Review SmartBear’s current restrictions.
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Visual differences appear across environments
First confirm that the differences are not expected consequences of target-specific rendering, viewport, or page state. Review visual baselines and the captured state used for comparison; a screenshot difference is a signal to investigate, not automatically a functional defect.
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Does cross-browser testing always use real browsers?
No. Some approaches execute automation in selected browser environments; Applitools describes a separate visual workflow that renders captured DOM and CSS data in parallel. Match the method to whether you need to test browser interactions, compare visual output, or both.
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Can the same test run in multiple browsers?
Often, if the framework supports multiple browser targets and the test uses compatible operations. Playwright’s project configuration is one example; remote testing tools may have their own requirements for selectors and supported test types.
Is “Ultrafast” the general name for parallel testing?
It is sometimes used informally, but it is also part of Applitools’ product naming. The DOM/CSS capture and parallel-rendering workflow described above is Applitools-specific.
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