What Is Selenium?

Yes. Selenium is open source under the Apache License 2.0, which allows free use, including commercial use, with no license fee and no seat count (Selenium on GitHub). The project sits with the Software Freedom Conservancy, a non-profit, and is built by volunteers and contributors from many companies (selenium.dev). There is no paid edition of Selenium itself.

Selenium does have running costs, and they are where "Selenium pricing" questions come from:

So the answer to "is Selenium free" is: the software is, and the infrastructure is what you budget for.

Selenium automates what a person does in a browser, so it is used wherever that needs to be repeated:

• Automated testing. Its main use: end-to-end and cross-browser tests of web apps, run in CI on every change.
• Web scraping. Loading pages that build their content with JavaScript and reading the rendered data; see web scraping with Selenium.
• Monitoring. Scripted checks that log in, search or check out on a schedule and alert when a step fails or slows down.
• Repetitive web tasks. Filling the same forms, downloading reports from a web portal, taking screenshots for records.

How Selenium WebDriver works

Your script calls the Selenium library, which sends each command (open a URL, find an element, click) as an HTTP request to a browser driver: chromedriver for Chrome, geckodriver for Firefox, msedgedriver for Edge, safaridriver for Safari. The driver performs it in the browser and returns the result. This protocol is a W3C standard, WebDriver, which became a W3C Recommendation in 2018 (W3C: WebDriver). Since Selenium 4.6, Selenium Manager finds or downloads the right driver for your browser automatically, so you no longer download chromedriver by hand (selenium.dev: Selenium Manager). Newer versions also speak WebDriver BiDi, a two-way protocol that adds events such as console logs and network activity.

How Selenium Grid works

Selenium Grid 4 receives new-session requests on one address (port 4444 by default) and routes each to a node that has the requested browser free. Inside, a router takes the requests, a session queue holds them, a distributor picks a node, and a session map remembers which node runs which session; nodes run the browsers (selenium.dev: Grid components). You can run it as one standalone process, as a hub with nodes, or fully distributed, and official Docker images exist for each part. Your script connects with a remote driver:

from selenium import webdriver
driver = webdriver.Remote(command_executor="http://localhost:4444", options=webdriver.ChromeOptions())

Python Selenium is the Python binding of WebDriver, the selenium package on PyPI. Install it with pip install selenium, and a few lines open Chrome, wait for content and read it:

# pip install selenium
from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC

options = webdriver.ChromeOptions()
options.add_argument("--headless=new")
driver = webdriver.Chrome(options=options)          # Selenium Manager finds chromedriver
driver.get("https://quotes.toscrape.com/js/")
WebDriverWait(driver, 10).until(EC.presence_of_element_located((By.CSS_SELECTOR, ".quote")))
for el in driver.find_elements(By.CSS_SELECTOR, ".quote .text"):
    print(el.text)
driver.quit()

The same API exists in Java, C#, Ruby and JavaScript, with the same concepts: a driver, find_element with a locator strategy (CSS, XPath, ID, name), explicit waits, and quit() at the end.

Selenium monitoring means running a scripted user journey (sign in, search, add to cart, check out) on a schedule against a live site and alerting when a step fails or takes too long. It catches problems a simple "is the site up" ping misses, such as a broken checkout button. Teams run the scripts from cron or CI against their own sites, or load Selenium IDE recordings and WebDriver scripts into a synthetic monitoring service. When you monitor from several countries, each run needs an IP in that country; a proxy with country and city targeting gives the browser that location.

All three drive real browsers; they differ in protocol and scope. Selenium uses the W3C WebDriver standard and supports the most languages and browsers, including Safari through Apple's driver. Playwright (Microsoft) and Puppeteer (Chrome team) talk to browsers over their own protocols, wait for elements automatically and intercept network traffic out of the box. For a new scraping project in Python or Node.js, many developers start with Playwright; teams with an existing Selenium test suite, a Grid or a language Playwright does not cover keep Selenium. More in what Playwright is and what Puppeteer is.