All charts and images must have alt text, or alternative text, to summarise what they are and show for users who cannot see them. Screen readers read this information out for people with visual disabilities. Alt text can also be used to describe what should be on the page if the web browser fails to load the images.
Alt text should include:
- the chart type (for example, bar chart, line chart or pie chart)
- the type of data in the chart (for example, marriage rates, level of GDP, or amount of weekly hours worked)
- a summary of the main trend of the chart
Alt text should:
- be around 125 characters (15 to 20 words) – it can be longer if needed, but if it is too detailed then include some content in the main text instead
- be no more than one sentence
- include a full stop at the end
- include any abbreviations written out in full
If your chart describes the trend
Your chart title should usually be a description of the data’s trend or highlight a main story. If this is the case, you can duplicate part of the descriptive chart title in the alt text.
When describing this chart, the alt text could read: A line chart showing the amount of weekly hours worked is still low but showing signs of recovery.
You can read more about our chart title guidance.
If your chart title does not describe the trend
If you do not have a descriptive chart title, you should first consider if your title could describe the data’s trend or highlight a main story. If it cannot, your alt text should still describe the trend where possible.
Your alt text summary should not:
- use a literal description of the chart – instead, focus on the point it is making
- repeat content in the main text – this causes “auditory clutter” for screen reader users where information may be repeated
- repeat information from the subtitle as screen readers will read this out too
If there is no data trend or story to highlight, you can use your chart’s title in the alt text even if it is not descriptive.