Selenium WebDriver zoom in/out page content

Beware that Selenium assumes the zoom level is at 100%! For example, IE will refuse to start (throws an Exception) when the zoom level is different, because the element locating depends on this and if you changed the zoom level, it would click on wrong elements, at wrong places.

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Java

You can use the Keys.chord() method:

WebElement html = driver.findElement(By.tagName("html"));
html.sendKeys(Keys.chord(Keys.CONTROL, Keys.ADD));

Use cautiously and when you're done, reset the zoom back to 100%:

html.sendKeys(Keys.chord(Keys.CONTROL, "0"));

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C#

(since I realized C# bindings don't have the Keys.chord() method)

Or, you can use the Advanced User Interactions API like this (again, Java code, but it should work the same in C#):

WebElement html = driver.findElement(By.tagName("html"));

new Actions(driver)
    .sendKeys(html, Keys.CONTROL, Keys.ADD, Keys.NULL)
    .perform();

Again, don't forget to reset the zoom afterwards:

new Actions(driver)
    .sendKeys(html, Keys.CONTROL, "0", Keys.NULL)
    .perform();

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Note that the naïve approach

html.sendKeys(Keys.CONTROL, Keys.ADD);

doesn't work, because the Ctrl key is released in this sendKeys() method. The WebElement's sendKeys() is different from the one in Actions. Because of this, the Keys.NULL used in my solution is required.

Here are two ways the zoom level can be altered with Java (one is for Chrome and the other is for Firefox):

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Chrome

When using v̲e̲r̲s̲i̲o̲n̲ ̲3̲.̲3̲.̲1 of the Selenium Java Client Driver and C̲h̲r̲o̲m̲e̲D̲r̲i̲v̲e̲r̲ ̲2̲.̲2̲8, the following works (where the number in single quotes represents the zoom level to use; 1 = 100%, 1.5 = 150%, etc.):

JavascriptExecutor executor = (JavascriptExecutor)driver;
executor.executeScript("document.body.style.zoom = '1.5'");

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Firefox

The zoom level can be modified with the following:
1. The aforementioned Java Client Driver
2. G̲e̲c̲k̲o̲D̲r̲i̲v̲e̲r̲ ̲v̲0̲.̲1̲5̲.̲0
3. These classes:
java.awt.Robot
java.awt.event.KeyEvent

First of all, instantiate the Robot class:

Robot robot = new Robot();

This code causes the zoom level to decrease:

robot.keyPress(KeyEvent.VK_CONTROL);
robot.keyPress(KeyEvent.VK_MINUS);
robot.keyRelease(KeyEvent.VK_CONTROL);
robot.keyRelease(KeyEvent.VK_MINUS);

This code causes the zoom level to increase:

robot.keyPress(KeyEvent.VK_CONTROL);
robot.keyPress(KeyEvent.VK_EQUALS);
robot.keyRelease(KeyEvent.VK_CONTROL);
robot.keyRelease(KeyEvent.VK_EQUALS);