Browser automation has evolved significantly as web applications have become more dynamic and distributed. Modern applications are no longer limited to static pages and simple user interactions. They rely on JavaScript, asynchronous operations, APIs, dynamic content, network requests, browser events, and continuously changing application states.
For teams using Selenium automation, this evolution creates a new challenge. It is no longer enough for a test to tell the browser what to do. Increasingly, automation needs to understand what is happening inside the browser while those actions are taking place.
A test may click a button and see nothing happen. An element may fail to appear because an API request returned an error. A page may fail because of a JavaScript exception. A workflow may become unreliable because of timing differences between browser events and application responses.
Traditional Selenium WebDriver provides powerful browser-control capabilities, but its fundamental interaction model is command-driven. The test sends a command to the browser and receives a response.
WebDriver BiDi introduces another dimension. Selenium BiDi enables bidirectional communication between the automation client and the browser, allowing automation to subscribe to browser events and receive information from the browser while the session is running. This changes the possibilities for browser automation testing.
But BiDi is not a replacement for Selenium WebDriver. Instead, it extends the WebDriver ecosystem with capabilities that are increasingly important for testing modern web applications.
To understand what Selenium BiDi changes, it is useful to first understand the traditional WebDriver model. Selenium WebDriver provides APIs that allow test scripts to control browsers programmatically. A test can instruct a browser to navigate to a URL, locate an element, enter text, click a button, switch between windows, or retrieve information from a page.
The simplified communication model looks like this:
Test Script → WebDriver → Browser → Response → Test Script
For example, when a test executes an action such as clicking a login button, the automation client sends the command through WebDriver. The browser processes the command and returns the result.
This request-and-response model works effectively for many browser automation scenarios. It provides the foundation for:
However, modern applications often require more visibility than a simple command-response interaction can provide. Consider a login page. A test enters valid credentials and clicks Login. The dashboard does not appear. The WebDriver test may report that an expected element was not found. But what actually happened?
Perhaps the authentication API returned a 500 response. Perhaps a JavaScript exception prevented the dashboard from rendering. Perhaps a network request was blocked. Perhaps a browser event occurred in an unexpected sequence. The UI failure is visible. The underlying browser activity may not be. This is one of the problems that WebDriver BiDi aims to address.
Selenium BiDi refers to Selenium’s implementation of WebDriver BiDi, the W3C standard for bidirectional communication between automation clients and browsers. The traditional WebDriver model is primarily command-based. BiDi adds an event-driven communication channel. The simplified model becomes:
Test Script ⇄ WebDriver BiDi ⇄ Browser
Instead of the test only sending instructions, the browser can also communicate information back to the automation client as events occur. These capabilities can include areas such as:
The result is a more observable automation environment. This matters because modern selenium bidi browser automation testing can potentially inspect browser behaviour beyond the visible state of the page.
The biggest change introduced by BiDi is not simply additional commands. It is visibility. Traditional automation primarily asks: “What should the browser do?”. BiDi makes it possible to additionally ask: “What is happening in the browser?”. That distinction becomes increasingly valuable when testing applications that depend heavily on asynchronous activity.
For example, imagine a checkout application. A user clicks Place Order. Behind the scenes, the application might:
If the confirmation does not appear, the final UI state alone may not explain the failure. Browser-level events can provide additional context around what happened during the interaction. This makes BiDi particularly interesting for teams trying to improve observability and debugging flaky selenium tests.
Selenium 4 represents the modern generation of Selenium and includes improvements across WebDriver, Grid, and browser integration. It is useful to think about the ecosystem as three complementary layers.
WebDriver provides the core browser-control mechanism. It handles actions such as:
BiDi adds bidirectional and event-driven capabilities. It can help automation interact with browser events and obtain additional information about activities such as logging and networking.
Grid addresses distributed execution. It allows tests to run across different machines, browsers, operating systems, and environments. These technologies therefore solve different problems. WebDriver controls. BiDi observes and communicates bidirectionally. Grid distributes. Together, they can form a powerful foundation for modern browser automation.
One of the most significant benefits of BiDi is the ability to work with browser events. Traditional UI automation often detects the consequence of a browser problem. For example:
Expected: Dashboard loads.
Actual: Dashboard does not load.
BiDi can potentially provide additional evidence about the sequence of events that occurred before that failure. For example:
User action → Network request → Server response → Browser event → JavaScript error → UI failure
This additional information can help engineers understand failures more quickly. Instead of treating the missing dashboard as an isolated UI problem, the automation framework can investigate the browser activity surrounding the failure. This is particularly useful for modern single-page applications where much of the application behaviour happens asynchronously without a full page reload.
Network activity is an important part of modern browser applications. A single page may communicate with dozens of APIs while the user interacts with it. For example:
Login → Authentication API → User Profile API → Permissions API → Dashboard API
A test may validate the final UI but have limited visibility into the network interactions responsible for producing that UI. BiDi introduces standardized capabilities for working with network events. This can support testing scenarios involving:
This can be particularly valuable when the UI behaves differently depending on backend responses. For example, instead of simply asserting that an error message appears, an automation workflow may also investigate whether the expected API interaction occurred. This brings browser automation closer to understanding the complete user interaction flow.
JavaScript is fundamental to modern web applications. A page can appear visually correct while still generating errors in the browser console. Conversely, a JavaScript error may prevent a component from rendering correctly.
Traditional UI automation may only discover the problem when a subsequent element cannot be located. BiDi can provide access to browser logging information and related events, allowing automation systems to capture additional browser-side evidence. This can be useful for:
For large regression suites, this additional information can reduce the amount of manual investigation required when failures occur.
Flaky tests are tests that produce inconsistent results without a corresponding intentional change in the application or test. A test may pass during one execution and fail during another. Common causes include:
BiDi does not automatically eliminate flakiness. What it can do is provide additional information that helps engineers understand the conditions surrounding a failure.
Suppose a test fails because an element does not appear. Without additional information, the investigation may focus entirely on the locator. With browser-level information, engineers may discover that an API request failed before the element could be rendered. That distinction matters. The problem may not be the Selenium test at all.
BiDi does not eliminate the need for good synchronization. Modern applications frequently update elements asynchronously. A test that immediately interacts with an element before the application reaches the required state can fail even when the application is working correctly. This is why Selenium explicit wait best practices remain important.
An implicit wait establishes a general waiting period when WebDriver attempts to locate elements. An explicit wait, on the other hand, waits for a specific condition. For example, a test might wait until:
Explicit waits are generally more targeted because they connect the synchronization logic to the condition the test actually requires.
Hard-coded delays such as:
Wait five seconds → Continue
are less reliable because application response times can vary.
BiDi complements synchronization rather than replacing it. Good automation still requires reliable locators, appropriate waits, deterministic test data, and well-designed test flows.
Dynamic elements are common in modern web applications. Element identifiers may change. Components may be rendered only after API responses. DOM structures may be updated dynamically.
Reliable Selenium automation should therefore avoid depending on fragile page structures whenever possible. Good practices include:
BiDi can provide additional browser context, but it does not replace sound test-design practices. The strongest approach combines reliable WebDriver automation with appropriate event and diagnostic capabilities.
Selenium has historically provided access to Chrome DevTools Protocol, commonly known as CDP. CDP provides powerful browser-level capabilities, particularly for Chromium-based browsers. However, CDP is a browser-specific protocol.
WebDriver BiDi is designed as a standardized approach to bidirectional browser automation. This distinction is important for teams that maintain cross-browser automation frameworks.
A framework heavily dependent on browser-specific functionality may require different implementations for different browser families. A standards-based approach can potentially provide greater consistency across supported browsers as browser implementations mature. This does not mean CDP suddenly becomes irrelevant.
Instead, BiDi represents a longer-term standards-oriented direction for bidirectional browser automation, while CDP remains useful for browser-specific capabilities where required.
Selenium Grid addresses a different challenge: scale. Consider an enterprise application that needs to be tested across:
Running every test sequentially can significantly increase execution time. Selenium Grid enables distributed WebDriver sessions so that tests can execute across multiple browser environments. This makes selenium grid 4 parallel testing particularly valuable for large regression suites.
BiDi can complement this architecture. A simplified model could look like:
Test Suite → Selenium Grid → Browser Session → WebDriver + BiDi
Grid determines where the test runs. WebDriver controls the browser. BiDi provides additional browser communication and event visibility. This combination can support a more scalable and observable browser automation environment.
Yes.Selenium can automate multiple browsers, and Grid can distribute those sessions across available environments. For example:
Test Suite
→ Chrome session
→ Firefox session
→ Edge session
These sessions can execute concurrently when the Grid infrastructure is configured with the necessary browser capacity. This makes Selenium particularly useful for cross-browser testing where teams need confidence that application behaviour remains consistent across different browser environments. BiDi can complement these sessions by providing browser-level information during execution.
A modern automation framework should not be built around UI interactions alone. A scalable framework should consider:
A possible architecture could look like:
Test Layer
↓
Automation Framework
↓
WebDriver + BiDi
↓
Selenium Grid
↓
Browser Infrastructure
The framework can also connect execution results with CI/CD systems, reporting platforms, logs, screenshots, and defect-management systems. The objective is to create an automation ecosystem where a failure does not simply produce a red test result. It produces useful evidence.
Flakiness can originate from several layers of the automation ecosystem.
The test interacts with an application before the required state is available.
The DOM changes between locating an element and interacting with it.
An API or external service responds slower than expected.
Parallel tests modify or depend on shared data.
Differences in browser versions, operating systems, infrastructure, or configuration affect execution.
Race conditions, asynchronous processing, or JavaScript errors cause inconsistent application states.
Weak locators, hard-coded delays, excessive dependencies, and poor test isolation can introduce instability.
BiDi can help investigate some of these conditions, particularly browser-side activity, but stable automation ultimately requires good engineering practices across the entire framework.
The most important change is the move toward browser observability. Traditional automation largely follows:
Command → Browser Action → Result
BiDi expands this into:
Command → Browser Action → Browser Events → Automation Response
That additional communication channel can change how teams approach:
Instead of only validating what the user can see, automation can increasingly investigate what happened inside the browser to produce that result. This is especially relevant as web applications become more asynchronous and distributed.
The role of a Selenium automation engineer is evolving alongside browser technology. Strong professionals should understand:
Selenium certification can provide structured learning for professionals who want to strengthen their Selenium knowledge, but practical experience remains critical. The modern automation engineer needs to understand not only how to automate a browser, but also how the browser, application, network, and test infrastructure interact.
Browser automation is moving toward a more event-driven model. Applications are becoming increasingly dynamic. Testing therefore needs greater visibility into application behaviour. WebDriver BiDi represents an important step in this direction.
Instead, it adds another capability to the Selenium ecosystem. WebDriver provides browser control. Grid provides distributed execution. BiDi provides bidirectional browser communication. Together, these capabilities can help teams build more capable automation systems for modern web applications.
Selenium has remained relevant because it has evolved alongside the web. The introduction of WebDriver changed browser automation by providing a standardized way to control browsers. Selenium 4 continued that evolution with improvements to the ecosystem and Grid architecture.
WebDriver BiDi takes the next step by making browser communication more interactive. The browser is no longer simply a system that receives commands from the test. It can also provide information back to the automation system about what is happening during execution. That opens up opportunities for richer network monitoring, browser-event handling, JavaScript error detection, and failure diagnostics.
For testing teams, the biggest opportunity is not simply to automate more actions. It is to build automation that understands more of the browser’s behaviour. As web applications continue to become more dynamic, this shift from browser control toward browser observability could become an increasingly important part of modern Selenium testing.
Selenium WebDriver communicates with browsers through the standardized WebDriver protocol. The automation client sends commands to the browser’s WebDriver implementation, which performs the requested action and returns a response. This enables Selenium to automate browser navigation, element interactions, windows, frames, cookies, and other browser operations.
Selenium BiDi is Selenium’s implementation of the WebDriver BiDi standard. It enables bidirectional communication between the automation client and browser, allowing automation to receive browser events in addition to sending commands. This can provide greater visibility into areas such as network activity, browser logs, and JavaScript-related events.
An implicit wait provides a general waiting period when WebDriver searches for elements. An explicit wait waits for a specific condition, such as an element becoming visible or clickable. Explicit waits are often more targeted for applications with dynamic content because they synchronize the test with a meaningful application state.
Selenium Grid allows WebDriver sessions to run across multiple machines and browser environments. This enables test suites to execute multiple tests concurrently and supports large-scale cross-browser and cross-platform testing.
Flaky Selenium tests can result from timing problems, unstable locators, dynamic web elements, asynchronous application behaviour, network delays, inconsistent test data, browser or environment differences, and genuine application issues. Poor synchronization and test-design practices can also contribute to flakiness.
Tests should use stable locators, meaningful synchronization conditions, and explicit waits where appropriate. They should avoid unnecessary hard-coded delays and fragile DOM dependencies. Test frameworks should also isolate test data and reduce unnecessary dependencies between test cases.
Yes. Selenium can automate multiple supported browsers, and Selenium Grid can distribute browser sessions across different environments so that tests can execute in parallel.
A Selenium automation engineer should understand WebDriver, Selenium 4, programming, locators, synchronization, test-framework architecture, Grid, parallel execution, CI/CD, cross-browser testing, debugging, API concepts, and increasingly WebDriver BiDi and browser-event concepts.
