Can you perform API Testing with Selenium?

API testing ensures that application programming interfaces work as expected. It checks if APIs deliver the right responses for given inputs and handle errors properly.

Selenium is primarily designed to automate user interface testing. While it can be adapted to handle API testing through custom code for HTTP requests, this approach involves workarounds that reduce effectiveness and limit the depth of API test coverage.

This article explains if and how to perform API testing with Selenium in detail.

Goals of API Automation Testing

Before discussing Selenium’s role in API testing, it is essential to clarify the key objectives that API testing must achieve. API automation must cover a range of concerns to ensure software quality and reliability.

API automation testing helps with:

• Functional testing: Verify APIs perform exactly what they promise under various input conditions. This includes confirming that valid inputs generate correct outputs and invalid inputs result in appropriate error responses.

• Protocol compliance: Ensure APIs adhere to expected HTTP standards, including the correct use of methods like GET, POST, PUT, DELETE, and proper status codes such as 200 (OK), 401 (Unauthorized), or 500 (Server Error). This ensures consistent communication patterns and helps clients interpret responses correctly.
• Data validation: Confirm that the format and structure of API responses match expected schemas, such as JSON or XML. This prevents downstream integration issues caused by malformed or unexpected data.
• Security validation: Test authentication and authorization mechanisms, ensuring only authorized users can access sensitive endpoints. Validate input sanitization to prevent injection attacks and other vulnerabilities.
• Performance and scalability: Measure response times and behavior under different loads to detect bottlenecks, latency issues, or failures under stress.

• Error and boundary handling: Test how APIs behave with unexpected, missing, or boundary input values. This reduces crashes and data corruption risks.
• Continuous integration readiness: Enable fast, repeatable tests that run automatically during development cycles to catch regressions early.

• Documentation alignment: Ensure API implementations match published specifications and documentation, which prevents integration mismatches.

Can Selenium Be Used for API Testing?

Selenium’s core purpose is to automate browsers to test web UI behavior. It simulates user actions like clicks, form filling, and navigation by interacting with HTML elements. This makes Selenium ideal for end-to-end UI workflows but not for direct backend service testing.

API testing requires sending HTTP requests directly, controlling headers and payloads, receiving complete HTTP responses including status codes and headers, and analyzing structured response bodies.

Selenium does not have built-in APIs to create or inspect raw HTTP requests and responses. It only interacts with what the browser exposes via the DOM or JavaScript execution.

Workarounds exist but are complex:

• Using JavaScript within Selenium to trigger XML HTTP Requests or fetch calls inside the browser.
• Monitoring browser network traffic via developer tools or proxy setups, but this is unreliable and brittle.
• Combining Selenium tests with separate HTTP clients for API calls in the same test suite adds architectural complexity.

In short, Selenium testing is useful for verifying API behavior indirectly by interacting with the UI that consumes the API, but not for deep API contract or performance testing.

Key Differences Between API Testing and UI Testing

API testing verifies backend services’ functionality, reliability, and performance without involving the user interface. UI testing checks the visual elements and user interactions in a web or mobile application.

Here is a table highlighting the differences between API testing and UI testing.

Limits of Selenium in API Testing

Selenium’s inability to perform direct HTTP operations limits its effectiveness for many API testing needs. Use Selenium for API testing only in cases where interaction must go through the UI or to validate end-to-end flows that combine UI and backend.

Consider these specific limitations:

• Isolated API validation: Selenium cannot send standalone HTTP requests without navigating through UI elements.
• Raw HTTP response inspection: It cannot access HTTP status codes or headers directly, which are essential for API correctness.
• Custom HTTP headers: Modifying or injecting headers like tokens or tracing IDs is not straightforward or well supported.
• Testing all HTTP methods: Selenium handles only GET via page loads; POST, PUT, DELETE, PATCH require indirect, complex workarounds.
• Edge case coverage: Many boundary tests involve unusual or malformed inputs not exposed through the UI.
• Performance and load testing: Selenium consumes significant resources and is too slow to load test APIs.

• Root cause identification: Selenium reports UI failures but cannot trace them back to specific API faults.
• Scaling parallel tests: Browser instances consume large resources, limiting how many tests can run concurrently.
• Generating API documentation: Selenium does not support creating API contract or schema documentation.

How to Set Up Selenium for Limited API Testing?

This method shows how to use Selenium to send API requests, capture responses, and validate data during your tests. It allows you to test APIs by executing JavaScript within the browser, monitoring network traffic, or calling APIs directly from your test code. Follow these steps to set up Selenium for API testing.

1. Use JavaScript Execution in the Browser to Send API Requests

You can send API calls directly inside the browser context by running JavaScript with Selenium’s executeAsyncScript (or executeScript). This lets you test APIs by sending requests and receiving responses via browser APIs like fetch or XMLHttpRequest.

Example in Java (using Selenium WebDriver):

// Cast driver to JavascriptExecutor

JavascriptExecutor js = (JavascriptExecutor) driver;



// Use executeAsyncScript for asynchronous fetch call

String apiResponse = (String) js.executeAsyncScript(

    "var callback = arguments[arguments.length - 1];" +

    "fetch('https://api.example.com/data', { method: 'GET' })" +

    ".then(response => response.text())" +

    ".then(data => callback(data))" +

    ".catch(error => callback('Error: ' + error))"

);



System.out.println("API Response: " + apiResponse);

2. Capture Network Traffic (Optional but Useful)

You can monitor and capture API request/response traffic from the browser during Selenium tests using tools such as:

• Chrome DevTools Protocol (CDP) integration with Selenium 4+
• Proxy servers like BrowserMob Proxy or MITMProxy
  Example: Using Chrome DevTools Protocol in Java to monitor network

DevTools devTools = ((ChromeDriver) driver).getDevTools();

devTools.createSession();



devTools.send(Network.enable(Optional.empty(), Optional.empty(), Optional.empty()));



devTools.addListener(Network.responseReceived(), response -> {

    System.out.println("URL: " + response.getResponse().getUrl());

    System.out.println("Status: " + response.getResponse().getStatus());

});

This lets you see all HTTP requests and responses while running tests.

3. Call APIs Directly from Test Code (Hybrid Approach)

Use an HTTP client in your test framework (separate from Selenium’s browser automation) to send API requests and validate responses directly. This can be used together with Selenium tests or standalone.

Example in Java with REST-assured:

import io.restassured.RestAssured;

import io.restassured.response.Response;



Response response = RestAssured.get("https://api.example.com/data");

int statusCode = response.getStatusCode();

String responseBody = response.getBody().asString();



System.out.println("Status code: " + statusCode);

System.out.println("Response body: " + responseBody);



// Add assertions as needed

assert statusCode == 200;

4. Validate API Responses Using Selenium Assertions (Optional UI Validation)

If needed, after calling APIs, you can use Selenium to validate UI changes or log results based on the API responses.

// For example, check if a UI element shows data returned by the API

WebElement element = driver.findElement(By.id("data-display"));

String displayedText = element.getText();

assert displayedText.contains("expected data from API");

Best Practices for Selenium API Testing

These best practices help improve test reliability, maintainability, and clarity and ensure your tests run smoothly.

• Separate API and UI Tests: Keep API calls and validations in distinct test methods or layers to maintain clarity and easier maintenance.
• Use JavaScript Execution: Leverage executeAsyncScript to run API requests inside the browser context when simulating client-side API calls.
• Integrate Network Traffic Monitoring: Use Chrome DevTools Protocol or proxy servers to capture and analyze HTTP requests and responses during tests for effective debugging.
• Use Dedicated HTTP Clients: Combine Selenium with libraries like REST-assured, OkHttp, or Python requests to call APIs directly from test code for faster and more reliable validation.
• Validate API Responses and UI States: Assert both API response content and corresponding UI updates for comprehensive test coverage.
• Handle Asynchronous Calls Properly: Use explicit waits or JavaScript callbacks to ensure API responses or UI updates complete before assertions to avoid flaky tests.
• Isolate Test Data and Environments: Use separate test data and API endpoints to avoid polluting production data and to improve reliability.

How to Use BrowserStack for Selenium Testing?

BrowserStack lets you run Selenium tests on a wide range of real browsers and devices hosted in the cloud. This helps you test your web applications across different environments without managing local infrastructure.

Follow these steps to get started with BrowserStack and Selenium:

1. Sign Up and Get Credentials

Create a BrowserStack account at browserstack.com. After signing up, find your Username and Access Key in the Automate dashboard under Settings.

2. Set Up Selenium WebDriver with BrowserStack

Configure your Selenium tests to connect to BrowserStack’s remote Selenium hub instead of running locally. Use your credentials and desired browser capabilities.

Example in Java:

import org.openqa.selenium.WebDriver;

import org.openqa.selenium.remote.DesiredCapabilities;

import org.openqa.selenium.remote.RemoteWebDriver;



import java.net.URL;



public class BrowserStackTest {

    public static final String USERNAME = "your_browserstack_username";

    public static final String AUTOMATE_KEY = "your_browserstack_access_key";

    public static final String URL = "https://" + USERNAME + ":" + AUTOMATE_KEY + "@hub-cloud.browserstack.com/wd/hub";



    public static void main(String[] args) throws Exception {

        DesiredCapabilities caps = new DesiredCapabilities();

        caps.setCapability("browserName", "Chrome");

        caps.setCapability("browserVersion", "latest");

        caps.setCapability("bstack:options", new HashMap<String, Object>() {{

            put("os", "Windows");

            put("osVersion", "10");

            put("local", "false");

            put("seleniumVersion", "4.0.0");

        }});



        WebDriver driver = new RemoteWebDriver(new URL(URL), caps);

        driver.get("https://www.example.com");



        System.out.println(driver.getTitle());



        driver.quit();

    }

}

3. Choose the Desired Browser and OS

Set browser, browser version, OS, and OS version capabilities to test on specific environments. BrowserStack supports many combinations, including Windows, macOS, Android, iOS, and popular browsers.

4. Run Tests on Real Devices or Browsers

BrowserStack runs your tests on actual machines in their cloud infrastructure. This ensures accurate testing on real hardware and browser behavior.

5. View Test Results and Debug

Use the BrowserStack Automate dashboard to view test logs, screenshots, and video recordings. This helps debug failed tests or UI issues quickly.

6. (Optional) Use BrowserStack Local for Testing Internal or Dev Environments

If your app runs behind a firewall or on localhost, use the BrowserStack Local binary to create a secure tunnel from BrowserStack to your environment.

Talk to an Expert

Conclusion

Selenium is excellent for UI automation but limited for API testing because it cannot natively manage HTTP requests and responses. API testing requires direct control over protocol-level interactions, data validation, and performance measurements that Selenium alone cannot provide.

Combining Selenium’s UI strengths with dedicated API testing tools or approaches ensures comprehensive coverage. Cloud platforms like BrowserStack boost Selenium’s capabilities by providing broad environment access and scalability.

Try BrowserStack for Free