To run HtmlUnit sessions through Selenium 4 Grid, install the HtmlUnit Remote Grid extension on the Grid server, configure a node slot with the htmlunit browser name, then connect from Java with RemoteWebDriver. HtmlUnitDriver alone is not the Grid integration: the HtmlUnit driver project directs Selenium 4 Grid users to HtmlUnit Remote.
This guide covers Java test suites using HtmlUnit as a GUI-less browser. HtmlUnit can be useful for suitable headless checks, but do not assume its behavior or rendering is equivalent to Chrome, Firefox, Safari, or another full browser your application supports.
What you need
- A Java test project and a Selenium Grid 4 server.
- The HtmlUnit driver dependency for local or client-side API use. The HtmlUnit driver repository currently lists
org.seleniumhq.selenium:htmlunit3-driver:4.48.0, dated September 2, 2026; consult the project’s README and compatibility tables before pinning a version. - The HtmlUnit Remote Grid extension JAR on the server. Selenium Server does not bundle the HtmlUnit driver artifacts.
- A Grid node configuration that advertises an
htmlunitslot and uses the HtmlUnit slot matcher.
The available sources do not establish a current HtmlUnit Remote artifact version or a complete compatibility range for Grid and driver versions. Verify the extension’s current release metadata and compatibility before choosing exact artifact filenames or declaring a specific supported combination.
Configure a Grid node for HtmlUnit
Save a TOML configuration such as htmlunit.toml. The names below follow the HtmlUnit Remote article; the driver and extension JAR versions must match verified release files.
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[node]
detect-drivers = false
[[node.driver-configuration]]
display-name = "HtmlUnit"
stereotype = "{"browserName": "htmlunit"}"
[distributor]
slot-matcher = "org.openqa.selenium.htmlunit.remote.HtmlUnitSlotMatcher"detect-drivers = false disables automatic driver detection for this node configuration. The explicit driver configuration registers a slot with the browserName value the client will request. The distributor’s slot matcher is the HtmlUnit Remote component that allows Grid to match that request to the configured slot.
Start Selenium Server with the extension
Place the Selenium Server JAR and the HtmlUnit Remote Grid extension JAR where you can reference them, then start the server with the extension loaded and the node configuration applied:
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java -jar selenium-server-<version>.jar
--ext htmlunit-remote-<version>-grid-extension.jar
standalone --config htmlunit.tomlReplace both angle-bracketed version strings with verified release versions and use the actual extension filename. This is the launch pattern shown by the HtmlUnit Remote guidance, not a claim that a particular extension version is compatible with every Selenium Server release. For a distributed Grid deployment, apply the extension and node configuration to the node that will provide the HtmlUnit slot, following the deployment layout you use for Grid.
Connect from a Java test with RemoteWebDriver
The client needs the Grid URL and browser options selecting the name advertised by the node. For a standalone server listening locally on the usual Grid endpoint, the Java test can be structured like this:
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import java.net.URI;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.remote.RemoteWebDriver;
import org.openqa.selenium.remote.MutableCapabilities;
public class HtmlUnitGridExample {
public static void main(String[] args) throws Exception {
URI gridUri = URI.create("http://localhost:4444");
MutableCapabilities options = new MutableCapabilities();
options.setBrowserName("htmlunit");
WebDriver driver = new RemoteWebDriver(gridUri.toURL(), options);
try {
driver.get("https://example.com");
System.out.println(driver.getTitle());
} finally {
driver.quit();
}
}
}Change http://localhost:4444 to the URL reachable by the test runner. Use the Selenium client dependency version selected for your project, and verify it against your Grid deployment. The code requests a remote session; it does not start Selenium Server or install the HtmlUnit extension.
Choose between local HtmlUnitDriver and Grid
| Mode | How it runs | Use it when |
|---|---|---|
| Local HtmlUnitDriver | The test instantiates and controls HtmlUnit in the test process. | You want a simpler local setup and do not need Grid-managed remote sessions. |
| Grid-managed HtmlUnit | The Grid server loads HtmlUnit Remote, a node advertises an HtmlUnit slot, and tests create sessions through RemoteWebDriver. | You need HtmlUnit sessions available through your remote Grid architecture. |
These modes share the HtmlUnit browser target but differ in where the session is created and managed. Whether HtmlUnit is an appropriate test target depends on what behavior the test is meant to establish. For compatibility or rendering confidence, include the real browsers your application supports rather than treating a GUI-less browser run as equivalent evidence.
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Version and compatibility checks
- Check the HtmlUnit driver project’s compatibility tables before selecting the driver artifact and HtmlUnit version.
- Check HtmlUnit Remote’s current release metadata for its Grid extension artifact and compatibility guidance.
- Confirm the extension JAR corresponds to the Selenium Server deployment you intend to run; the versioned names in the launch example are placeholders.
- Start the configured Grid and verify that a request for
browserName=htmlunitcan obtain a session before making the setup part of a larger test suite.
The HtmlUnit Remote setup article was published August 19, 2024. Its configuration and architecture are useful, but release metadata should be checked before relying on its example artifact naming for a current deployment. The HtmlUnit driver repository lists version 4.48.0 with a September 2, 2026 date; that driver listing by itself does not establish the matching HtmlUnit Remote extension version.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Troubleshooting
Grid cannot create an HtmlUnit session
- Check the server extension: confirm Selenium Server was started with
--extand the path resolves to the HtmlUnit Remote Grid extension JAR. - Check the node slot: verify that the node loaded
htmlunit.toml, its stereotype is valid TOML containing the JSON string forbrowserNamehtmlunit, and the slot matcher class is available from the extension. - Check the requested name: the Java client must request
htmlunit, matching the configured stereotype.
Server fails while loading configuration or extension
- Check the TOML section names and quoting, especially the escaped quotes inside
stereotype. - Check the extension file path and filename. The sample’s version placeholders are not literal filenames.
- Re-check extension and Selenium Server release compatibility; the cited setup material does not provide a current complete compatibility matrix.
Remote connection fails before session creation
- Confirm the Grid URL is reachable from the test process and points to the Grid endpoint, not to a URL available only from another host.
- Verify Selenium Server is running and listening at the configured address and port.
- If Grid is deployed across multiple hosts, ensure the node registering the HtmlUnit slot is connected to the Grid deployment your client contacts.
A test passes in HtmlUnit but fails in a real browser
Treat this as a browser-target difference to investigate, not proof that either result is universally correct. HtmlUnit is a GUI-less browser; the available project sources do not establish behavioral equivalence with full browsers. Reproduce the scenario in the real browsers relevant to your application before drawing compatibility conclusions.
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Or skip the browser setup
If your goal is a page screenshot rather than a WebDriver test session, ScreenshotNeo offers a one-request screenshot API; it is not a replacement for HtmlUnit-based test automation or Selenium Grid. See the ScreenshotNeo API documentation.
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://example.com -o shot.webpScreenshotNeo accepts cookie or consent banners before capture and removes more than 60 known consent platforms, newsletter popups, and chat widgets; each step can be turned off. Bot checks or CAPTCHAs, blank pages, timeouts, failed loads, and cache hits are not billed, with response headers indicating the page verdict and billing status. It also provides an MCP server for AI agents, with screenshot, page-info, and PDF-capture tools. The Free plan includes 1,000 screenshots per month with no card; paid plans start at $5 for 3,000 shots.
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Frequently Asked Questions
Can I use HtmlUnitDriver directly with Selenium 4 Grid?
Use HtmlUnit Remote for the Grid integration; HtmlUnitDriver alone is the local WebDriver-compatible driver.
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No equivalence is established by the cited project materials. Use real supported browsers for browser-specific compatibility and rendering checks.
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