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For new Selenium automation, use WebDriver BiDi to subscribe to browser network events. Register the listener before the action you want to inspect, then trigger that action and examine the event data. Use a request or response handler instead when a test must modify or block traffic; that is interception, not passive observation. BiDi setup and API details vary by language binding, Selenium version, and browser.
Choose observation or interception
“Capture network requests” can mean two different things. Decide which result you need before writing the test:
- Observe: receive events about requests and responses so you can log, inspect, or assert on traffic without deliberately changing it.
- Intercept: pause or handle traffic so the test can change request headers or body, block a request, or work with an incoming response. This changes the traffic path, so the test is no longer observing only what the page would ordinarily send and receive.
Selenium describes WebDriver BiDi as the bidirectional WebDriver protocol that lets the controlling program receive browser events. Its network features require BiDi to be enabled in the browser options before you use the network API. Register event handlers before triggering the page action: an event stream should not be treated as a store of events from before the subscription.
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Selenium’s forward-looking route for network events is WebDriver BiDi. Selenium’s documentation describes it as “the W3C standard bidirectional protocol for browser automation, created by the Selenium project together with the browser vendors.” Actual network support still depends on the browser’s implementation and the particular Selenium language binding. The setup and callback shape are not interchangeable assumptions across Python, Java, JavaScript, and other bindings.
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Python example: observe requests
The following is a Python-shaped example for the API documented by Selenium 4.43.0. It illustrates the event-handler approach; check the API reference for the installed Selenium release and browser before relying on exact event fields or callback details. The example enables BiDi, registers a before-request handler, then navigates so the navigation’s requests occur after registration.
from selenium import webdriver
options = webdriver.ChromeOptions()
options.enable_bidi = True
driver = webdriver.Chrome(options=options)
requests_seen = []
def on_request(event):
# Inspect the event structure for your Selenium binding/version.
requests_seen.append(event)
print(event)
try:
driver.network.add_request_handler(
"network.beforeRequestSent",
on_request,
)
driver.get("https://example.com")
print(f"Captured {len(requests_seen)} request event(s)")
finally:
driver.quit()Install Selenium in the environment that runs the script and ensure the matching browser and driver are available to Selenium. This sample uses Chrome as the browser example; BiDi is the protocol direction, but the exact option, network object, event representation, and supported events depend on binding and browser. Treat the event as structured data, not as a guaranteed string format. Log only fields you need once you have confirmed their names for your installed version.
Which events answer which question?
The Selenium Python 4.43.0 API reference lists these network event names:
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- BACKLIT LCD DISPLAY: Backlit LCD screen displays cable length, wiremap, cable ID, and test results, ensuring easy readability in various lighting conditions
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network.beforeRequestSent— inspect a request as it is about to be sent.network.responseStarted— observe the beginning of a response.network.responseCompleted— observe completion of a response.network.fetchError— observe a fetch failure event.
Choose the earliest event that contains the information your assertion needs. A before-request event is suited to checking what the browser is sending; response events are better suited to response lifecycle checks. Event payloads and field names are binding-specific, so inspect the API reference for the version you actually run rather than copying field access from a different language.
Filter events when possible
The Python 4.43.0 handler API accepts an event, callback, optional URL patterns, and optional browsing contexts. Filtering to the relevant URL patterns or context can make test logs easier to read and reduce irrelevant processing. Confirm the expected pattern and context syntax in the version-specific reference. If a test needs all traffic, omit those optional filters rather than using an overly broad or incorrect pattern.
Intercept traffic only when the test requires it
BiDi network handler APIs can also intercept outgoing requests and incoming responses. Depending on the handler, a test can alter request headers or body, block a request, or inspect and modify response data such as headers, status, or content. These are useful for controlled cases—for example, testing how a page behaves when a resource is blocked—but the modified transaction is not an unaltered record of normal browser traffic.
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- PORT FLASHING:The indicator light on the connection port in the NF-8508 device flashes to help accurately locate the cable. Displays port information, including operating speed, duplex mode, and negotiation settings. Port lights flash on the same screen to show the port's operating speed, making it easy to pinpoint lines and ports.
- PoE Testing and Cable Length Test: PoE testing can check cable mapping polarity and voltage of PoE network switches, withstand 60VDC. Automatically detects and switches between 10M/100M/1000M modes, Includes cable tracking, short circuit test, interruption of circuit test and etc The RJ45 cable tester can quickly measure the length of the cable with a range of 200m. Not only network cables, but also phone lines and BNC cables.
Keep observation and interception separate in test design. Use passive event subscriptions for assertions about ordinary page behavior. Use an intercepting handler when the test explicitly needs a changed request or response, and make the change obvious in the test name and setup so later maintainers do not mistake modified traffic for production behavior.
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For Chrome- or Edge-oriented automation, Selenium also exposes Chrome DevTools Protocol functionality, including a documented NetworkInterceptor example. CDP is tied to Chromium DevTools support. Selenium cautions that CDP was not designed as a stable testing API, that functionality depends heavily on browser version, and that its CDP access is temporary while WebDriver BiDi is implemented.
That makes CDP a reasonable option for maintaining an existing Chromium-only suite or using a capability you already depend on, but a weaker default for a new cross-browser test. Align and pin the Selenium and browser versions in CI, and budget for migration work if the suite depends on CDP-specific behavior. Do not assume a CDP example will transfer unchanged to BiDi.
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Pick the path that matches the test
| Need | Starting point | Important qualification |
|---|---|---|
| Stream browser network lifecycle events for a new test | WebDriver BiDi network events | Enable BiDi in options first; verify support for the browser, language binding, and Selenium version. |
| Change or block requests or responses deliberately | BiDi request or response handler | This changes the traffic being tested; use it for controlled interception scenarios. |
| Maintain Chromium-specific automation already using DevTools | Selenium CDP functionality, such as the documented NetworkInterceptor example | Version-sensitive, Chromium-oriented, and described by Selenium as temporary while BiDi is implemented. |
Make captured traffic useful in tests
Subscribe before the action
Start the driver, enable BiDi, and register the event callback before navigation or the click, form submission, or other action whose requests matter. Otherwise, the test may miss early events because it subscribed after they were emitted.
Scope the capture
Prefer URL patterns and browsing-context filters when they match the test’s purpose. If you collect every event, avoid dumping all payloads into routine CI logs: traffic can be noisy and may contain sensitive values such as tokens, cookies, or user data. Log only what an assertion needs, and redact secrets before storing artifacts.
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Assert on stable properties
Test meaningful behavior—such as whether a required endpoint was contacted or whether a response lifecycle event occurred—rather than relying on incidental request ordering. Pages can issue unrelated analytics, image, font, or third-party requests, and timing can vary. Keep test assertions scoped to the endpoint and event relevant to the feature under test.
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Troubleshooting
- No events arrive: confirm BiDi was enabled in browser options before creating the session, that the browser supports the feature, and that the handler was registered before the navigation or action. Verify the event name and handler method against your binding’s installed-version documentation.
- The option or network API is missing: the code may target a different Selenium binding or release. Check the binding’s BiDi setup instructions and API reference; examples from another language or version may use different names or callback shapes.
- Some requests are absent: check whether your URL-pattern or browsing-context filters exclude them. Also verify that your subscription began before the triggering action; do not assume earlier events are buffered.
- Fields in the callback do not match the example: event payloads are version- and binding-specific. Inspect the actual event object and the API reference for your release instead of assuming another binding’s field layout.
- CDP behavior changes after an upgrade: Selenium documents CDP as version-sensitive. Align the Selenium and browser versions, and consider moving new functionality to BiDi where the browser and binding support it.
- A test sees different traffic after adding a handler: determine whether the handler is intercepting and modifying or blocking requests. Use an observation subscription when the test needs ordinary, unmodified traffic.
Performance, reliability, and maintenance
Capturing events adds work to the automation process: the browser emits event data and the test callback must process it. Keep callbacks short, filter where appropriate, and avoid retaining large response bodies unless the test needs them. This is a practical test-design precaution, not a Selenium performance benchmark; the cited Selenium material establishes no general throughput or overhead figure.
For reproducibility, record the Selenium binding and version, browser and version, and whether the test uses BiDi or CDP in the project’s dependency and CI configuration. Browser support and protocol compatibility can change, and language bindings do not necessarily expose the same surface at the same time. Recheck the binding API when upgrading rather than treating one code sample as universal.
Or skip the browser setup
If the goal is a page image rather than inspecting its network traffic, ScreenshotNeo offers a one-request screenshot API. It does not capture or expose network requests, so it is not a substitute for Selenium BiDi or CDP when network events are the requirement.
cURL:
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpPython:
import requests
r = requests.get("https://api.screenshotneo.com/v1/shot", params={"access_key": "YOUR_API_KEY", "url": "https://stripe.com"}, timeout=90)
open("shot.webp", "wb").write(r.content)Node.js:
const q = new URLSearchParams({ access_key: 'YOUR_API_KEY', url: 'https://stripe.com' });
const res = await fetch(`https://api.screenshotneo.com/v1/shot?${q}`);See the ScreenshotNeo API docs for request options. Cookie banners, newsletter popups, and chat widgets are removed before the shot; bot checks, blank pages, and failed loads are never billed. Its MCP server lets AI agents take screenshots. The free plan includes 1,000 screenshots a month with no card, and paid plans start at $5 for 3,000.
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