How to write alt text for charts and graphs

Charts are where alt text most often goes wrong in one of two ways. Either it says almost nothing ("Bar chart") or it tries to read out every bar and label until the listener gives up. Good chart alt text sits between the two: it says what kind of chart it is, what it is about, and what it shows. The data itself, when someone needs it, goes somewhere better suited to data.

The pattern: type, subject, takeaway

Most chart alt text can follow the same three parts:

Type. "Bar chart", "Line graph", "Pie chart", "Map". This tells the listener how the information is organised.
Subject. What is measured, for whom, over what period. "Monthly sales in 2026", "Share of commuters by mode of transport".
Takeaway. The trend, comparison or outlier the chart was made to show, with the few numbers that support it.

The Nielsen Norman Group makes the same point in Alt Text: What to Write: charts can look complicated, but their main point is often simple, and that point is what the alt text should carry. Ask yourself what you would say if you showed the chart to someone across a table. That sentence is usually the takeaway.

Examples by chart type

The charts in these examples are made up for illustration.

Bar chart

Weak: "Bar chart."
Weak: "Bar chart with five bars, blue, the first is 12, the second is 18, the third is 9, the fourth is 22, the fifth is 15."
Good: "Bar chart of library visits by weekday. Saturday is busiest with about 2,200 visits, more than twice Monday's 1,000. The other weekdays fall between 1,200 and 1,600."

Colours and bar order only belong in the alt text if they carry meaning, for example when the post refers to "the red bars".

Line graph

Good: "Line graph of a café's average daily customers over one year. Numbers are lowest in January at about 60 a day and climb to a peak of about 140 in August."

For a line graph, the shape over time is usually the point: rising, falling, flat, a peak, a sudden drop. Say the shape in words and give the start, end or peak values.

Line graph with several series

Good: "Line graph comparing a bike shop's sales of e-bikes and standard bikes from 2020 to 2026. E-bike sales rise every year and pass standard bike sales in 2025. Standard bike sales fall steadily over the period."

With more than one line, the relationship between the lines is the takeaway: one overtakes the other, they move together, or they diverge.

Pie chart

Good: "Pie chart of how a household budget is spent. Housing takes the largest share at 35 percent, followed by food at 20 percent. Transport, bills and savings each take 10 to 15 percent."

Name the largest parts and roughly how big they are. You do not need every small slice unless it matters to the post.

Map

Good: "Map of a city's twelve districts shaded by tree cover. The northern districts have the most trees, and the city centre and the industrial east have the fewest."

For maps, describe the pattern across places rather than the value for each region.

Infographic

Infographics combine charts, icons and text. Treat them like a short document: give the title, then the main points in order.

Good: "Infographic titled 'Three ways to save water at home'. 1: Turn off the tap while brushing your teeth. 2: Fix dripping taps. 3: Run the dishwasher only when full."

If an infographic has more than a handful of points, the NN/g article suggests putting its information in the page or post text as a list, which helps everyone, not only screen reader users.

When the data matters: add a long description

Sometimes the reader needs more than the takeaway: a report, a dashboard, a chart people will make decisions from. The W3C's tutorial on complex images recommends a two-part approach for these:

A short alt text that identifies the chart and, where needed, says where the full description is: "Bar chart of quarterly visitors for sites 1 to 3, described in detail below."
A long description with the values, scales and relationships, ideally as a data table or text near the chart, visible to everyone.

WebAIM's alternative text guide gives the same advice: when a chart's content will not fit in a succinct alt attribute, provide it elsewhere, such as a data table on the same page or a linked page, and keep the alt text describing the general content.

On a website, that long description can be a table under the chart or a link to the data. On social media, there is no table, but there are still options:

Put the key figures in the post text or in a reply, and say so in the alt text: "Figures in the reply."
Link to the source, such as the report or dataset the chart comes from.
Use the room you have. Bluesky allows 2,000 characters of alt text and X allows 1,000. A chart with a few values can fit them all. See alt text character limits for each platform.

Common mistakes

Describing the look instead of the meaning. "A colourful chart with blue and orange bars" says nothing a listener can use.
Leaving out the numbers entirely. "Sales went up" is better than nothing, but "Sales rose from 400 to 650 units" is what the chart actually shows.
Including every number. A list of 24 values read aloud is hard to follow. Pick the ones that support the takeaway and offer the rest elsewhere.
Stating a conclusion the chart does not show. If the chart shows sales rising, the alt text should not say why. Explanations belong in your post.
Forgetting titles and axis labels. If the chart has a title, start with it. If the axis units are unusual, such as thousands or percentages, say so.
Forgetting the source and date when they are part of the image. If the chart says "Source: city council survey, 2026", include it.

A quick check before you post

Read your alt text without looking at the chart. Can you answer these?

What kind of chart is it?
What is being measured, and over what period or group?
What is the one thing the chart shows?
Are the key numbers there and correct?

If any answer is missing, add it. If the description has grown past three or four sentences, consider moving the detail into a long description and keeping the alt text to the takeaway. The guide on how long alt text should be covers this balance in more detail.

Charts with AltKit

AltKit is set up to give the takeaway for charts: the trend or comparison, not only the chart type. In the web creator, signed-in users can add context, for example "chart for our quarterly report, focus on the change since last year", and AltKit uses it where it fits what the chart shows. Check every number it quotes against the chart before you publish, as you would with your own draft.