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What capabilities do in Selenium
Capabilities describe the browser and configuration requested when a WebDriver session starts. For a local session, the browser-specific Options object carries those settings to the driver. For a remote session, the server uses the request to find a browser configuration it can provide. A requested feature that the remote end cannot provide can cause session creation to fail.
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In Selenium 4, options are the supported way to configure a session. Selenium 3 examples often built a DesiredCapabilities object and supplied it separately; when updating that code, move the settings to the matching Options object instead of carrying the old pattern forward. See Selenium’s Selenium 4 upgrade guide.
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Set capabilities for a remote session in Python
This example requests Firefox with a particular browser version and operating-system platform. Replace the endpoint and requested values with ones your Grid actually supports; the example has not been run against a real Grid.
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-
Install Selenium in the Python environment used for the test:
python -m pip install selenium. -
Set the requested values on Firefox’s
Optionsobject. -
Pass that object to
webdriver.Remotealong with the Grid’s command-executor URL.Special offer. See more information about Outbyte and uninstall instructions. Please review EULA and Privacy policy.
from selenium import webdriver
from selenium.webdriver.firefox.options import Options
options = Options()
options.set_capability("platformName", "windows")
options.browser_version = "142"
driver = webdriver.Remote(
command_executor="http://grid.example:4444/wd/hub",
options=options,
)
try:
driver.get("https://example.com")
print(driver.title)
finally:
driver.quit()grid.example:4444/wd/hub is an example endpoint, not a public Selenium service. The browser version and platform also need to match configurations available on your Grid. Selenium’s Python API documents the Options-based remote pattern here: Python Desired Capabilities API, Selenium 4.49.0.
Set a capability locally
The same principle applies to a local driver: create the browser’s Options instance, set the desired values, and pass it to that browser’s driver constructor. For example, use webdriver.Chrome(options=options) with a ChromeOptions instance. Do not pass a standalone legacy DesiredCapabilities object as the Selenium 4 setup pattern.
Use current W3C capability names
Selenium 4 follows the W3C WebDriver standard. Common standard capability names include:
| Capability | What it requests or configures |
|---|---|
browserName |
The browser type, such as Firefox or Chrome. |
browserVersion |
The requested browser version. |
platformName |
The operating-system platform. |
acceptInsecureCerts |
Whether the session should accept insecure certificates. |
pageLoadStrategy |
When navigation is considered complete for WebDriver. |
proxy |
Proxy configuration. |
timeouts |
Session timeout settings. |
unhandledPromptBehavior |
How the session handles unexpected user prompts. |
Use browserVersion and platformName, not the older version and platform names. The Selenium upgrade guide explains these W3C naming changes and capability migration: Upgrade to Selenium 4.
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Configure browser-specific and provider-specific options
Use the browser Options class for standard values and browser-specific settings supported by that class. Remote Grid and cloud providers may also accept extension capabilities, but those are not interchangeable across vendors. Selenium’s migration example places a provider’s build and name fields inside a vendor namespace such as cloud:options; check your provider’s current documentation for the exact prefix, nesting, and supported values.
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A non-standard field in the wrong namespace or structure can make the remote server reject session creation. Do not assume that a setting accepted by one cloud provider will work unchanged on another.
Choose a page-load strategy deliberately
The page-load strategy changes when WebDriver returns from navigation; it does not guarantee that a JavaScript-heavy application has finished its later, dynamic work. Selenium documents these three strategies:
| Strategy | When navigation returns | Trade-off |
|---|---|---|
normal |
After the document reaches ready state complete and resources have downloaded. |
Waits for more of the page’s initial resource loading, which can take longer. |
eager |
When the document reaches ready state interactive. |
The DOM is ready, but resources such as images may still be loading. |
none |
WebDriver does not block on page loading. | Returns control sooner, but the page may not yet be ready for the next test action. |
normal is the default. eager or none can be useful when waiting on nonessential assets dominates navigation, but these settings apply to the whole session. Keep explicit waits for the specific element or application state your test needs; navigation returning is not a substitute for waiting on dynamic content. See Selenium Browser Options.
Troubleshoot capability and session errors
-
Session creation fails after a Selenium 4 upgrade: replace the legacy DesiredCapabilities setup with the browser’s Options class and pass it through the driver’s
optionsargument. -
The server reports an invalid or unsupported capability: check for legacy names such as
versionorplatform; usebrowserVersionorplatformNamefor the standard W3C fields. -
A vendor setting is rejected: verify the provider’s required vendor prefix and nesting. Keep provider extensions separate from standard capability names.
-
The requested browser cannot be matched: confirm that the remote endpoint has the requested browser name, version, and platform, and that the combination is available there. Remote session negotiation fails when the endpoint cannot satisfy the request.
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The test acts before the page is ready: a faster page-load strategy may return while resources are still loading, and even
normaldoes not wait for all later single-page-app activity. Add an explicit wait for the condition the test needs.
For remote capability matching, the WebDriver model distinguishes required features from alternatives: alwaysMatch expresses requirements that must be satisfied, while firstMatch lists alternatives considered in order. See MDN’s WebDriver capabilities reference.
Or skip the browser setup
If the task is to capture a website screenshot rather than run browser interactions or assertions, ScreenshotNeo is a screenshot API and MCP server for developers. It is not a Selenium replacement for automating a test. One GET request returns an image or PDF, without setting up a WebDriver session:
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)See the ScreenshotNeo API documentation for request options. Before capture, it accepts cookie or consent banners and removes more than 60 known consent platforms, newsletter popups, and chat widgets; each of those steps can be turned off. Bot checks or CAPTCHAs, blank pages, timeouts, failed loads, and cache hits are not billed, and responses identify the page verdict and billing status in headers. Its MCP server provides take_screenshot, get_page_info, and capture_pdf tools for AI agents. 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
What does alwaysMatch mean in a WebDriver capabilities request?
It contains required features; if the remote end cannot provide them, session creation fails.
Can I use Selenium page-load strategy to know when a single-page app has finished loading?
No. It controls when navigation returns, not when the application’s later dynamic work is complete.
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