What is accessibility?

Website accessibility describes whether a website can be used by people of all abilities. Good accessibility makes it simple for every user to find, use and understand content. 

Publishing web content in HTML makes it accessible to as many people as possible across all devices. It also allows for users who need to change the way they view the web page, for example, changing the size of the text or colour contrast.

A good measure of whether web content is accessible is to make sure users can:

  • perceive and understand it, whether through sight, sound or touch
  • operate using screen readers, voice activation software, high contrast, and other tools with ease
  • understand the content written in plain English
  • access the content with all browsers and devices

Text and hyperlinks

  • Write all content in plain English, and explain all abbreviations and jargon.
  • Include a summary or bullet points of the main information at the beginning of the content.
  • Try to make paragraphs no more than two or three sentences, breaking up the text into short chunks.
  • Use headings and subheadings to break up sections of text and create structure.
  • Use bullet points for all lists of three things or more.

It is important to write simply and consider the reading order of your content so that it flows naturally. If you are unsure, test your content by asking someone to read through it to make sure the language and order makes sense.

Avoid using italics or bold, underlining text and overuse of capital letters, as the text could be mistaken for a heading and large amounts can be hard to read for users with visual impairments. Instead, create emphasis through what you write.

Do not use directional text, such as “click here” or “the list below”, as this could be misleading for people using various tools to browse the website.

When creating hyperlinks, the text containing the link should be a specific description of the destination page. Ideally, links should be placed near the end of a sentence so that users can take action immediately, rather than having to remember to go back.

There is more information about accessibility within GOV.UK content if you are interested.

A further explanation is provided in the full terms and conditions.

Assistive technologies separate out links, so each one should be easy to identify and clearly tell the user where the link will take them.

accessibility within GOV.UK content

full terms and conditions

If a hyperlink will involve downloading a file rather than going to another web page, users should be informed what type of file they are about to download and its size.

In July we published a new user guide for population statistics (PDF, 100KB)

Quotation marks are not needed around a hyperlink.

Alt text

All charts and images must have alt text, or alternative text, to summarise the information presented for users who cannot see the visual. It can also be used to describe what should be on the page if the web browser fails to load the images. Screen readers read this out for people with visual disabilities.

Alt text should be around 125 characters (15 to 20 words), be no more than one sentence and include:

  • the chart type used
  • the type of data used in the chart
  • a summary of the main trend of the chart

Avoid using a literal description of the image or chart and instead focus on what point it is making. Alt text can duplicate part of the descriptive chart title but should not repeat content in the main text.

When describing this chart, the alt text could read: Line chart of marriage rates where the amount of opposite-sex marriages peaked in 1972 and has generally fallen since.

Line chart of marriage rates where the amount of opposite-sex marriages peaked in 1972 and has generally fallen since.

Charts

  • All content in charts (such as axes, keys and other labels) must display horizontally and be easy to read.
  • Ensure axis labels are displayed in full and not cut off or abbreviated.
  • Write out abbreviations in full or clearly explain them in the footnotes.
  • Make sure there is a clear distinction between different lines, by using different line types or colour shades that can easily be distinguished when viewed in black and white – bear in mind that different colours can be more or less perceivable depending on the shape and context of the chart.
  • If the axis includes dates, these must be consistently displayed for all charts in the release so that they are easy to follow.
  • The key must always display above the chart for easy reference.

An interactive HTML chart should always be used rather than an image of a chart. This ensures that all users are able to read it, including those with assistive technology such as screen readers. 

Interactive charts will also adapt to the size of the screen being used to view the content, so they are more useful to users accessing the content on a mobile or tablet.

Chart titles should be descriptive and clearly explain what the data are showing.

Avoid using dual axis charts as they are often misleading and difficult to understand. Either use separated charts or a single axis chart which uses annotations to explain the trends.

Tables

  • These should only be used to present data, not lists of text.
  • Important information should be displayed first.
  • Abbreviations should be written out in full or clearly explained.
  • Column headings in tables should be clearly visible.
  • Decimal rounding should be consistent throughout the table.
  • Ensure there are no blank rows or columns.
  • Do not use any bold or italic formatting.
  • Numbers should be right-aligned, text should be left-aligned.

The size of a table can have a big impact on how easy it is for users to read and understand it. Consider whether the information can be better presented in the text as a bulleted list or split into headings and subheadings. 

An increasing amount of users view data on a mobile or tablet, so narrow tables are preferred to wide tables. As a guide, three to four columns can fit onto an average smartphone screen without too much scrolling.

Large tables containing a lot of data may be better presented as a dataset (downloadable spreadsheet).

Images, maps and infographics

Images can be useful to illustrate a point, but they should not be used as a replacement for a clear text description.

Images must be no more than 600 pixels wide but can be longer than 600 pixels. Always consider usability when determining the length of an image; it needs to be fully visible on-screen without too much scrolling.

Do not use text in images. If it cannot be avoided, the same text must be explained as a long description nearby on the page or in the alt text. This is so that it can be changed into other forms such as braille, speech or symbols. 

Avoid using colour alone to convey meaning in an image, as users with visual disabilities can find it hard to distinguish between them. Using red and green together is a common example as many people are unable to tell these colours apart. If you have to use colour to help explain something – check it with colour blindness software.

Maps with multiple clickable areas should provide an explanation in the alt text or in the text nearby that gives an overall context to the meaning of the map.

Video, audio and interactive content

We do not currently support audio and visual content on the website.

This can present barriers for some users, but it can enhance accessibility for others. Some users may prefer to access data in a non-text-based format.

When presenting data in an interactive format (for example, SVG), provide the data being used to create the animation as a downloadable file in CSV or XLS format. Give a description of the main points where possible.

When using audio or video content, always provide a transcript and captions. If the content is also on a third-party website, provide it there if possible. For example, on YouTube you should provide a transcript in the comments section and an option to turn on closed captions. As well as being helpful for users with visual or hearing disabilities, it allows all users to download the information for offline use to read in their own time. 

When using video or audio content, avoid flashing lights and images, which can cause seizures, and keep distracting background noise to a minimum.

Diagrams

Before using a diagram consider whether the message can be communicated better through text or a table, as users often find process maps and flowcharts difficult to understand.

If there is a user need to provide a diagram instead of a text explanation, it must:

  • have a clear starting point
  • follow normal reading direction, from left to right and top to bottom
  • avoid having overlapping lines or arrows
  • use simple shapes

As diagrams are usually uploaded as PNG files, they must also follow the same guidance for using images, including as little text as possible.

All diagrams must be created by Digital Publishing. There is further guidance on how to format your information and get in touch available.

PDF content

We do not publish PDF-only content on the website, as research has shown that users find them more difficult to use than web pages. PDF files are less accessible than web flat pages, or HTML pages, so PDFs should not be used without a flat page alternative.

If a PDF is necessary, such as in older survey guidance, then make sure PDFs are altered to meet accessibility standards. You can check this using the accessibility checker in Adobe Acrobat Pro. You should also check your PDF is accessible with a screen reader. 

The PDF should have:

  • correctly tagged content within Adobe (such as headings, text, tables and images) so screen readers can understand the structure
  • the correct reading order within Adobe
  • alt text added to all images
  • bookmarks for all main headings in the navigation pane and the PDF file set to open this pane automatically
  • all content written in plain English following ONS house style conventions
  • the language specified (usually English)
  • consistent font size and line length throughout

We are constantly improving based on research and best practice. Any significant changes to our guidance are available on the Updates page.