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Alternative Text for Images

About Alternative (Alt) Text

Alternative text (commonly known as alt text) describes visual elements on a webpage or document. Describing images with alt text gives context for people using screen readers so they can access that content.

Tip: As a best practice, alt text descriptions should be 120 characters or less. This is usually one or two short sentences. Make sure to convey the meaning being expressed in the image.

In addition to images on HTML pages, alt text is also used to describe images that are within the following content formats:

  • Documents
  • PDFs.
  • Tables
  • Infographics

All images need descriptions

For infographics, graphs, charts, maps or illustrations that are complex images of text, which often contain detailed graphic imagery or charts, instead of alt text use a complex text description to describe all meaningful information within the content. 

  • To create a complex text description, start by placing alt text on the image defining what it is and stating that a long description is adjacent to the image.
  • Also provide a long description adjacent to the image that conveys all of the information within the image of text. If this information already appears in the text, then it is not needed as a long description.

For PDFs of visually designed items like brochures or postcards, refer to the How To guide for PDFs.

For graphic elements that are purely decorative and don't add information to the page, such as icons, borders, spaces or some logos, you can use a null or empty alt attribute written like this: (alt=""). 

Not sure what type of image description to use? This alt text decision tree from W3C can help.

Tips for Writing Alt Text Descriptions

  1. Don't use "photo/image of" — Because screen readers and other assistive devices already describe images as such, you don't need to preface alt text with "Image of" or "photo of."
  2. Use simple, descriptive language when writing alt text to give the reader a clear idea of what the image depicts.
    1. Close your eyes and think of the image and include information that you'd use to describe it.
  3. Keep it relevant — Limit the alt text description to relevant information; you don't have to include every single nuance of an image, just the main details of it.
    1. Consider the purpose of the image on the page. Include the relevant information it's being used to convey.
  4. Be concise — A phrase or one or two short sentences are usually sufficient.
    1. Note that some screen readers may stop reading alt text after around 120 characters.
Web Content Authors: Learn how to add accessible images to the Aims website

Learn More About Writing Alt Text for Images and Documents