Text size, Style, Blinking Elements and Readability

Readability focuses both on the way the web page has been designed as well as the content. Some research has shown that those who show a reluctance to reading online feel there is an impact on comprehension levels so clarity, layout with good use of white space as well as text size and style are all important


Text blinking, flashing and other fast moving animations can also problems for those with photosensitive epilepsy as noted by Epilepsy Action

Authors need to explain acronyms, complex vocabulary and obscure terms that may not be recognised by some readers with the offer of a glossary or links to explanations.

The text size, style and other features relating to the appearance of web pages tend to follow fashion and depend on the language being used. In English some users prefer sans serif fonts such as Arial or Helvitica to serif fonts such as Times New Roman. It is a subject that is much debated even by those developing the UK government website A few notes on typography


It is easy to see whether an item is flashing or blinking and causing distraction. The test can be completed manually. Try to work through a whole site as there may be many pages with different types of flashing content – it is often the advertisements that blink. If you have concerns download the Trace Photosensitive Epilepsy Analysis Tool (PEAT)

The image below is taken from the Lings Cars website that has flashing content, clutter, animation, music, mixed fonts and much more.

cluttered, complex and flashing text

The checks need to include the fact that the text is real text and not a graphic that cannot be read by a screen reader.  The fonts need to be a good size (“Clear print fonts have a minimum type size of 12 point” RNIB).  The style should be simple with good contrast levels as mentioned in the contrast checks.  

It is hard to find specific advice as to which are easiest to read fonts (Webaim offer examples of sans serif fonts) or the right size but there must be the opportunity for users to make changes (background and text colour as well as size).

The ability to make these changes can be tested using the ATbar. It is also possible to use browser ‘options’ to change these features as described in the archived BBC My Web My Way.

font changes

Checking for Readability in terms of being able to understand content may depend on the aim of the website. There are online tests with scores for the number of complex multisyllabic words used in sentences as well as sentence length based on the Fog and Flesch Scales as provided by Juicy Studio.   There is also the Literacy Trust page on How can I assess the readability of my document or write more clearly that may help with the checks.



This technique may be used to test the following sections of best practice.

Document Section Heading
WCAG 2.0 2.3 Do not design content in a way that is known to cause seizures. More Info
WCAG 2.0 2.3.1 Three Flashes or Below Threshold More Info
WCAG 2.0 3.1 Make text content readable and understandable. More Info

See Also

WCAG 2.0: Guideline 2.3 Seizures: Do not design content in a way that is known to cause seizures. Understanding Guideline 2.3

2.3.1 Three Flashes or Below Threshold: Web pages do not contain anything that flashes more than three times in any one second period, or the flash is below the general flash and red flash thresholds. (Level A) Conformance Requirement 5: Non-Interference. How to Meet 2.3.1 | Understanding 2.3.1

Guideline 3.1 Readable: Make text content readable and understandable. Understanding Guideline 3.1