How do screen readers work?

Screen readers are software programs that allow those who have difficulty reading printed text, or interpreting icons, access to content.

People who are completely blind are the primary users of screen readers. That being said, they can also be used by people with dyslexia, low vision, or by anyone who may not be able to look at a screen.

Illustration: Profile shot of user with headphones

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“While a sighted person can glance at a screen and understand content as a whole, someone listening to a screen reader cannot.”

Things screen readers have in common

While the exact operation differs from screen reader to screen reader, and platform to platform, all screen readers have the following things in common:

  • They depend on text: As pieces of software, screen readers generally cannot make sense of graphical content. For this reason, alt-text on images, and labels on icons, are crucial.
  • They read content in a linear fashion: Screen readers generally read out the contents of the screen using text to speech. While a sighted person can glance at a screen and understand content as a whole, someone listening to a screen reader cannot. Making sure focus is managed correctly, and tab order is set up properly, helps give the screen reader a linear pathway to navigate your website.
  • They provide shortcut keys to make navigating easier: Shortcuts help users to quickly navigate using the semantic structure of  a website. For example, all screen readers allow users to skip directly to the next and previous heading or the next and previous link/button. If you have not provided this semantic information, screen reader users will become confused.

Things that change from platform to platform

Mobile screen readers are quite different from desktop screen readers. On desktop, a screen reader user may navigate by using the tab key, arrows, or other shortcut keys on the keyboard. On mobile, screen readers define special touchscreen gestures instead of keyboard commands. For example, swiping left or right with a single finger, always moves to the next or previous element on the screen.

Mac and Windows screen readers are also slightly different. By default, Windows screen readers will intercept every keystroke a user makes, and attempt to interpret it as a command. Only if the keystroke is not a screen reader command, will it be passed on to a website. If a Windows user wants to pass keystrokes on to the browser, they must indicate this by placing the screen reader into a specific mode. On a Mac, all screen reader commands require the user to hold down a special key combination (usually command + option), leaving all other keystrokes free for the OS and web browser.

Common vocabulary

When reading feedback from screen reader users, or having meetings with screen reader users, here are some terms you might encounter, and what they mean:

  • “Forms mode”, or “focus mode”: Used by Windows screen readers, if a user wants to type into an edit field, activate controls like checkboxes/buttons/combo boxes, or use any shortcut keys a web application defines, they must first place their screen reader into “forms mode” or “focus mode”.
    • Example: “When I was in forms mode, I couldn’t use the spacebar to check any of the checkboxes.”
  • Elements list: Most screen readers provide a function that will list every element of a particular type in a listbox, allowing the user to explore, and be taken directly to listed items. For example, a user who wants to skim your website for something, or a user who is looking for a particular link might use the links list.
    • Example: “I opened the links list, but because none of the clickable items on the website were marked as links, I had a hard time finding what I was searching for.”
  • Swipe: A single finger swipe is the gesture used by mobile screen readers to move from one element to the next.
    • Example: “I couldn’t swipe to any of the controls in this app.”
  • Double tap: All mobile screen readers require the user to double tap on anything to activate it. If a user single taps, the screen reader will announce the element the user just engaged with. This is helpful so they know what they will activate should they double tap.
    • Example: “I double tapped the submit button several times, but nothing seemed to happen.”

Popular screen readers

  • VoiceOver: Made by Apple, VoiceOver runs on iPhones, Mac computers, Apple Watches, Apple TV’s, and iPods. Apple does not allow third party screen readers, so it is the only screen reader used on any Apple product.
  • Talkback: An Android screen reader, developed by Google. While Google does allow third party screen readers on Android, TalkBack is by far the most popular option, as it comes built-in to most Android devices.
  • NVDA (Non-Visual Desktop Access): A free, open-source screen reader, developed for Windows. Because of its open source nature, it is highly customizable. It is extremely popular with technical users, as well as users who may not otherwise have access to a Windows screen reader.
  • JAWS (Jobs Access With Speech): Another extremely popular Windows screen reader. While it is more costly, the easy availability of support and training materials, high level of acceptance in the corporate environment, and its focus on working with business apps, makes it the preferred choice for many Windows users.