Alternative text (alt text)

Alternative text gives images and other non-text content a text version that serves the equivalent purpose.

What is alternative text (alt text)?

Alternative text is the text version of content that is not itself text. WCAG 2.1 defines a text alternative as text that is programmatically associated with non-text content, or referred to from text that is programmatically associated with it. Guideline 1.1 "Text Alternatives" states the aim: content should be changeable into other forms people need, such as large print, braille, speech, symbols or simpler language.

Under WCAG 2.1, non-text content is any content that is not a sequence of characters that can be programmatically determined, or where the sequence does not express something in human language. This expressly includes ASCII art, emoticons, leetspeak and images representing text.

Success Criterion 1.1.1 (Level A) requires a text alternative that serves the equivalent purpose. It sets out these special cases:

• Controls and input: if non-text content is a control or accepts user input, it needs a name that describes its purpose. Further requirements are in Success Criterion 4.1.2.
• Time-based media, tests or exercises that would be invalid if presented in text, and content primarily intended to create a specific sensory experience: the text alternative must at least provide a descriptive identification of the content.
• CAPTCHA: the text identifies and describes the purpose. Alternative forms using other types of sensory perception are also required.
• Decoration, formatting, invisible content: such content must be implemented so that assistive technology can ignore it. According to WCAG 2.1, pure decoration serves only an aesthetic purpose, provides no information and has no functionality.

Legal bases and references

The yardsticks are WCAG 2.1 and the standard EN 301 549 V3.2.1. The references at a glance:

According to clause 10.0, clause 10 applies to documents that are not web pages, to documents that are not embedded in web pages, and to documents that are provided with web pages but are neither embedded nor rendered together with them, that is, to downloadable documents. Note 1 to clause 10.0 gives letters, spreadsheets, emails, books, pictures and presentations among its examples. Note 7 to clause 10.0 makes clear that the requirements also apply to documents protected by digital signatures, encryption, passwords or watermarks when they are presented to the user.

Annex A, Table A.1 (No. 82), maps clause 10.1.1.1 to the essential requirement "perceivable" of Directive (EU) 2016/2102, for documents and forms that are downloadable from a web page. Under Annex A, once the standard is cited in the Official Journal of the EU under that Directive, conformance with the normative clauses in Tables A.1 and A.2 confers, within the limits of the scope of the standard, a presumption of conformity with the corresponding essential requirements. How the yardsticks fit together is explained in the article on PDF/UA, WCAG 2.1 and EN 301 549. See also WCAG 2.1 and EN 301 549.

Practical example

Where EN 301 549 is the yardstick, every piece of non-text content in a PDF annual report, a Word template or a PowerPoint presentation needs a text alternative, unless an exception under Success Criterion 1.1.1 applies. This is how you handle typical cases:

1. Chart: a short text alternative indicates that a description follows. The description sits in the paragraph after the chart. WCAG 2.1 gives this approach as an example in its definition of a text alternative.
2. Image containing text, such as a scanned notice: it needs a text alternative, because WCAG 2.1 classifies images representing text as non-text content.
3. Decorative lines and background graphics: if they serve only an aesthetic purpose, with no information and no functionality, they are pure decoration. They must be implemented so that assistive technology can ignore them.
4. Graphical buttons, such as in a PDF form: if non-text content is a control, it needs a name that describes its purpose. Further requirements for controls are in Success Criterion 4.1.2.

For verification, EN 301 549 provides an inspection for clause 10.1.1.1 (Annex C.10.1.1.1). Further checkpoints are in the checklist for Word and PowerPoint. Closely related are the tagged PDF and the reading order. If you prefer not to rework your files yourself, you can have accessible documents prepared.

See also

• WCAG 2.1 (Web Content Accessibility Guidelines)
• EN 301 549 (harmonised standard for ICT accessibility)
• Tagged PDF (tag structure)
• Reading order