Block Specific Resources in Playwright

I’ve seen Playwright tests slow down for reasons that have nothing to do with the app logic.

Extra scripts loading.

Third-party calls stalling.

Fonts and trackers eating time on every run.

When a test flakes, I always ask myself-is this really a test issue, or just unnecessary network noise? Blocking specific resources in Playwright helps take that uncertainty out of the equation and brings control back to the test run.

This article explains how to block specific resources in Playwright to reduce network noise, speed up test runs, and make results more predictable-without breaking core user flows.

What Does Blocking Specific Resources Mean in Playwright?

Blocking specific resources in Playwright refers to intercepting browser network requests and deciding, at runtime, whether those requests should be allowed or aborted. Modern web pages trigger a large number of background requests that are not essential for validating user flows.

Key aspects of resource blocking include:

• Intercepting outgoing network requests before they reach the server, allowing tests to control what the browser loads
• Preventing non-essential assets such as analytics scripts or decorative images from slowing page navigation
• Allowing tests to proceed without waiting for third-party services that do not affect functional behavior
• Shifting test execution from being network-dependent to behavior-focused, improving determinism

This mechanism gives testers explicit control over the browser’s loading behavior instead of relying on default network conditions.

Why Testers Need to Block Resources in Playwright?

Automated tests frequently fail due to external dependencies rather than actual defects in the application.

Common reasons testers block resources include:

• Third-party services responding slowly or intermittently, causing navigation or wait conditions to time out
• Network latency differences between local machines and CI environments introducing inconsistent behavior
• Parallel execution in CI amplifying minor delays into widespread flakiness
• Difficulty diagnosing failures when test logs are cluttered with unrelated network errors

Blocking resources reduces noise and ensures failures are more likely tied to application logic.

Common Scenarios Where Resource Blocking Improves Test Stability

Certain testing scenarios are especially vulnerable to network-related instability.

• Login and authentication flows that trigger analytics, fraud detection, or identity scripts which delay redirects
• Checkout and payment journeys where third-party integrations affect page readiness
• Single-page applications that load monitoring scripts on every route change, interfering with timing assertions
• CI pipelines operating under restricted or shared network conditions
• Large regression suites where small delays compound across hundreds of tests

In these cases, resource blocking isolates the test flow from factors it does not need to validate.

Types of Resources You Can Block in Playwright

Playwright supports blocking resources based on request metadata, URL patterns, or custom logic.

Commonly blocked resource types include:

• Third-party JavaScript files used for analytics, ads, chat widgets, or A/B testing tools
• Images that are purely decorative and not required for interaction
• Fonts loaded from external CDNs that add latency without affecting functionality
• Media files such as videos and animations that significantly increase load time
• Tracking pixels and beacon requests triggered during page lifecycle events
• Background API calls unrelated to the test objective, such as telemetry or monitoring endpoints

Each resource category should be evaluated based on its impact on test behavior.

How To Block Specific Resources in Playwright Using Route Interception

Playwright’s route interception feature allows fine-grained control over network requests during test execution.

Core concepts of route interception:

• Matching requests using wildcard patterns or specific URLs
• Inspecting request attributes such as resource type, method, or headers
• Deciding whether to abort or continue requests programmatically
• Applying interception rules globally, per test file, or within individual test cases

Example:

await page.route(‘**/*’, route => { const type = route.request().resourceType();

if (type === ‘image’ || type === ‘font’) {

route.abort();

} else {

route.continue();

}

});

This setup ensures only functional assets are loaded while visual assets are skipped.

Blocking Third-Party Scripts and Analytics Requests

Third-party scripts are among the most common causes of flaky tests because they depend on external systems outside test control.

Reasons to block third-party scripts:

• They load asynchronously and can delay page load completion signals
• Failures in these scripts rarely indicate application defects
• They introduce unpredictable timing variations across environments
• They add unnecessary console errors and warnings to test logs

Typical blocking strategies include:

• Matching known analytics or tracking domains
• Blocking ad networks and customer engagement widgets
• Preventing experimentation or feature-flag scripts from executing during tests
• This keeps test execution aligned with core user functionality.
• Blocking Images, Fonts, and Media Files for Faster Test Runs
• Visual assets significantly increase page load time and resource usage.

Benefits of blocking visual assets include:

• Faster navigation and reduced waiting time for page readiness
• Lower memory and bandwidth consumption during test execution
• More consistent execution times across local and CI environments

Commonly blocked asset types:

• Images such as banners, icons, and background graphics
• Fonts loaded from third-party CDNs
• Media files including videos, animations, and audio clips

This strategy is ideal for functional and regression tests where visual fidelity is not under validation.

Allowing Only Required Network Requests (Whitelist Approach) in Playwright

A whitelist approach flips the usual network-blocking strategy on its head. Instead of blocking a few known third-party resources, everything is blocked by default and only explicitly allowed requests are permitted. This is especially useful when tests need to be deterministic, fast, and isolated from external dependencies.

This approach is commonly used when:

• Tests must run without relying on third-party services
• External scripts or trackers introduce flakiness
• Only a small, known set of APIs is required for a test to function
• Frontend behavior needs to be validated independently of backend noise

How the Whitelist Approach Works

Playwright allows interception of all network requests at the browser level. With a whitelist strategy:

• Every outgoing request is intercepted
• Requests matching approved URLs or patterns are allowed
• All other requests are aborted immediately

This ensures the application loads only what the test explicitly depends on.

What to Whitelist

A good whitelist is intentionally minimal. Typically, it includes:

• The application’s main domain
• Required API endpoints used by the test flow
• Authentication or session-related calls
• Static assets that are critical for rendering (if needed)

Everything else-analytics, ads, third-party widgets, fonts, or media-can be safely blocked.

Benefits of the Whitelist Approach

Using a whitelist instead of selective blocking provides clearer guarantees.

Key advantages include:

• Faster test execution by eliminating unnecessary downloads
• Reduced flakiness caused by slow or failing third-party services
• More predictable test behavior across environments
• Easier debugging since only expected requests are in play

This is particularly valuable in CI pipelines, where network instability can cause intermittent failures.

When to Use Whitelisting vs Blacklisting

Whitelisting is most effective when:

• The application has a limited number of required network calls
• Tests focus on specific user flows rather than full-page fidelity
• Stability and speed matter more than visual completeness

Blacklisting is often better when:

• The application depends on many dynamic APIs
• Blocking only known troublemakers (ads, analytics) is sufficient
• Full-page rendering needs to stay closer to production behavior

Choosing between the two depends on how tightly controlled the test environment needs to be.

Scaling Whitelist-Based Tests

As test suites grow, maintaining whitelists manually can become difficult. Patterns and configuration files are often used to centralize allowed domains and endpoints. When tests run at scale-especially on real browsers and devices-platforms like BrowserStack help validate that whitelisted behavior remains consistent across environments without reintroducing unwanted network dependencies.

Handling Dynamic or Conditional Resource Blocking in Playwright

Different tests require different levels of realism, and Playwright supports dynamic blocking logic.

Common conditional blocking strategies:

• Enabling aggressive blocking only in CI environments
• Disabling blocking for visual, accessibility, or performance tests
• Applying different rules to smoke, regression, and exploratory suites
• Using environment variables or test metadata to toggle blocking behavior

This flexibility prevents one-size-fits-all rules from limiting test coverage.

Debugging and Validating Blocked Requests in Playwright

Validation is critical to ensure resource blocking does not break required functionality.

Useful debugging practices include:

• Logging all aborted requests to understand what is being blocked
• Monitoring failed requests to detect accidental over-blocking
• Reviewing network activity when tests fail unexpectedly
• Adjusting patterns incrementally rather than blocking broadly

Example:

page.on(‘requestfailed’, request => { console.log(‘Blocked:’, request.url());

});

This visibility makes it easier to refine blocking rules safely.

Best Practices for Blocking Resources Without Breaking Tests in Playwright

Resource blocking must be applied carefully to avoid masking issues.

Recommended practices:

• Block only resources that have no functional impact on the test scenario
• Avoid blocking backend APIs unless responses are intentionally mocked
• Centralize blocking logic in shared setup or fixtures
• Maintain documentation of blocked domains and resource types
• Review and update blocking rules as application dependencies change

When resource blocking is pushed into real-world environments, execution consistency becomes critical. BrowserStack Automate helps validate blocked-request strategies on real browsers and devices, ensuring that aggressive blocking rules do not break critical flows in production-like conditions.

By running Playwright tests at scale with full network visibility, Automate makes it easier to confirm that performance optimizations remain stable across browsers and platforms.

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Scaling Resource Blocking in CI Pipelines

CI pipelines benefit the most from resource blocking due to shared infrastructure and parallel execution.

Key scaling considerations:

• Apply blocking rules globally through test setup to ensure consistency
• Combine blocking with parallel workers to reduce overall build time
• Standardize network behavior across environments
• Minimize non-deterministic failures caused by external services

This leads to faster pipelines and more reliable feedback cycles.

Common Mistakes to Avoid When Blocking Resources in Playwright

Improper blocking can introduce subtle issues.

Common pitfalls include:

• Blocking critical JavaScript files that silently break application logic
• Aborting API calls instead of explicitly mocking responses
• Applying overly broad blocking rules without test-level overrides
• Ignoring blocked-request logs when diagnosing failures
• Treating resource blocking as a substitute for performance testing

Avoiding these mistakes ensures blocking improves stability rather than hiding problems.

Why use BrowserStack to test Blocked Resources in Playwright?

Using BrowserStack to test blocked resources in Playwright helps ensure that network-level optimizations behave correctly outside local or emulated environments. Blocking requests can speed up tests, but it can also introduce subtle failures that only appear under real browser and device conditions.

BrowserStack is useful for this scenario because:

• It runs Playwright tests on real browsers, helping confirm that blocked resources do not break rendering or script execution in production-like environments
• Differences in browser engines and versions can affect how blocked requests are handled, which BrowserStack helps surface early
• Network behavior on real devices can expose race conditions or missing dependencies that local setups often hide
• Built-in logs, screenshots, and videos make it easier to trace failures caused by over-blocking
• Parallel test execution allows teams to validate blocking rules across multiple browsers without slowing test cycles

This makes BrowserStack especially valuable when resource blocking moves from a local optimization to a strategy used in CI and release pipelines.

Try BrowserStack Automate

Conclusion

Blocking specific resources in Playwright removes unnecessary network dependencies that slow tests down and introduce flakiness. By selectively intercepting non-essential requests, test runs become faster, more predictable, and easier to maintain.

When applied thoughtfully and reviewed regularly, resource blocking strengthens Playwright test suites without compromising confidence in application behavior.