Accessibility tools and testing
Understand test results
- Last reviewed
- 24 August 2026
- Owner
- DesignOps
Learn how to check accessibility test results, identify false positives and avoid false assurance.
Accessibility testing tools can help you identify potential barriers, but they cannot understand every aspect of your content or how it works for people. You need to validate test results and carry out manual checks to identify false positives and avoid false assurance.
Understand false positives
A false positive is an issue flagged by an accessibility testing tool that is not actually an accessibility issue when you review it manually.
Accessibility testing tools cannot understand all the context of your content. For example, they may not understand:
- the purpose of link text
- whether an image needs alternative text
- the information an error message needs to provide
- whether a contrast issue applies to exempt content, such as a logo
Contrast in images
Some accessibility testing tools may flag contrast issues for exempt content, such as logos and branding.
Logos may not always have sufficiently contrasting foreground and background colours, but they are not required to meet these criteria. This is a false positive.
Review the result manually to check if the content needs to meet the relevant contrast requirements.
Understand false assurance
Accessibility testing tools can also give a false sense of compliance. They cannot identify every accessibility issue, so a test can pass even when a barrier remains.
Accessibility testing tools typically identify around 30% to 40% of accessibility issues. This means a service can pass automated testing while still having accessibility barriers.
Example: false assurance with alt text
Alt text should describe the purpose or meaning of an image when this information helps users understand the content.
When testing images for alt text, an automated tool may check whether an image has an alt attribute. It cannot determine whether the description accurately reflects the image.
This can give false assurance. An image with alt text may pass the automated check even when the text is not descriptive or meaningful.
For example, an image of a classroom with alt="car" or alt="image123" could pass a basic automated check because an alt attribute is present. However, the description does not provide meaningful information about the image.
Do
Ensure alt text accurately describes the image. alt="A teacher standing in front of a class of children who are sitting at desks." [add image]
Do not
Do not use a filename or misleading descriptions. alt="image123" [add image]
If you're unsure whether to use alt text
Use the alt text decision tree to check whether you need to provide alt text.
You do not need to add alt text when an image is purely decorative and does not add context to the page. In this case, use an empty alt attribute: alt="".
Check your test results
Do not rely on automated testing alone. Review flagged issues manually and carry out additional manual or specialist testing where appropriate.
Testing with people who have different access needs can also help you identify barriers that automated tools cannot detect.
See [Find and use tools] for guidance on the tools and techniques you can use to test for accessibility.