How do you write good alt text for a chart?
Most researchers have never written alt text, and most guides only say that it should be "meaningful". This page shows how to write it: six steps, one pattern, and examples for a bar chart, a micrograph, a multi-panel figure, a flowchart and a scatter plot, each with a weak and a good version side by side.
It covers the writing only. Standards, law, AI tools, software settings and costs are in Alt Text for Scientific Figures: The Complete Guide. When the finished document has to become an accessible PDF, the PDF accessibility service of DTP Services Berlin builds your descriptions into it.
What should alt text do?
A screen reader reads the alt text aloud in place of the figure. It should give a blind reader what a sighted reader takes from the figure in a few seconds: what kind of figure it is, what it shows and what the main result is[1, 2]. Blind readers in research studies wanted the figure type first, then numbers and trends, and no editorialising[3, 4].
Everything that takes longer to explain, such as all values, every panel or the steps of a process, goes into a long description in the visible text or a data table. In a PDF, alt text is one plain string of text; it cannot hold lists or tables[5].
How do you write it, step by step?
Six steps for every figure
- Find the point. Ask: what should a reader take away from this figure? Write it down in one sentence, for yourself.
- List what is in it. Figure type, variables, axes and units, groups, panels, scale bar.
- Look at the data behind the picture. Note the main values, the range, extremes and the size of the differences.
- Write the alt text. Use the pattern: type, what is measured, main finding with numbers, where the details are. One to three sentences.
- Write the long description. Axes and ranges first, then the pattern, then what stands out. Add a table when readers need exact values.
- Check. Compare every number with your data. Read the alt text aloud without looking at the figure: does it make sense?
Example 1: a bar chart
Figure 1A placeholder. The reader learns nothing.Bar chart showing the results of the study.Names the type, but not what was measured or found.The middle bar is the highest.Position instead of content. Which group? How high?Flipped classrooms clearly improve learning.An interpretation, not a description.
Bar chart of mean exam scores by teaching method: flipped classroom 71 points, project-based 68, lecture 62. Details below the figure.
134 characters. Type, what is measured, the three values in a useful order, and a pointer. The error bars are left to the long description.
The long description
The chart compares three teaching methods with 30 students each, on a score scale of 0 to 100. Mean exam scores were 71 points for the flipped classroom, 68 for project-based teaching and 62 for lectures. Error bars show 95% confidence intervals: 67 to 75 for the flipped classroom, 64 to 72 for project-based teaching and 58 to 66 for lectures. The intervals for the flipped classroom and lectures do not overlap; the others overlap.
Observation, result or interpretation?
Research figures make these easy to mix up. A chart shows values. Whether a difference is significant comes from your analysis, and what it means is your conclusion. Keep the three apart:
| Type of statement | Example | Where it belongs |
|---|---|---|
| Observation: what the chart shows | "Mean scores were 71 points with the flipped classroom and 62 with lectures." | Alt text and long description |
| Result: what your analysis found | "The difference between flipped classroom and lectures is statistically significant (p = 0.002)." | Long description or caption, only if it is in your results |
| Interpretation: what you conclude | "Flipped classrooms improve learning." | Your discussion section, not the figure description |
Blind readers in a peer-reviewed study rated statistics and trends as the most useful parts of a chart description, and most did not want the author's interpretation in it[4].
More examples from research
The pattern stays the same for every figure type. The examples below have no image; a short note describes the figure, followed by a weak and a good version.
A micrograph
The figure: two fluorescence microscopy images of cultured nerve cells, untreated (left) and treated (right). The study's point: treated cells grow longer branches. Scale bar 50 µm.
Microscope image of cells.No method, no comparison, no point.Green and blue structures on a black background with many thin lines.Describes colours and shapes, not what they show.
Fluorescence micrographs of cultured nerve cells, untreated (left) and treated (right): treated cells have visibly longer branches. Scale bar 50 µm.
Method, sample, the comparison and the point of the figure. Measured branch lengths belong in the text or a table, not in a list of everything visible[6].
A multi-panel figure
The figure: Figure 3 has three panels. A: map of 12 river sampling sites. B: bar chart of species counts per site. C: scatter plot of species count against water temperature.
Figure 3 A to C.A label, not a description.Panel A shows a map with 12 dots, panel B shows bars of 14, 9, 22, 17, 11 … and panel C shows …Everything crammed into the alt text. Nobody can follow it.
Three-panel figure on river sampling: a map of 12 sites (A), species counts per site (B) and species count against water temperature (C). Panel-by-panel description below.
One alt text for the whole figure, describing its purpose[7]. The long description then goes panel by panel and says how the panels relate: "Panel C shows that the sites with the lowest counts in B are the warmest"[5].
A flowchart
The figure: a flowchart of a sampling procedure with five steps and one loop back when a sample fails the quality check.
Flowchart of the sampling procedure in five steps, from site selection to laboratory analysis, with one loop back after a failed quality check. Steps listed below.
The long description is a numbered list, which a screen reader user can navigate step by step[8]:
- Select the sampling site.
- Take three water samples.
- Run the quality check. If a sample fails, return to step 2.
- Label and cool the samples.
- Analyse the samples in the laboratory.
A scatter plot
The figure: species count against water temperature for 12 sites, with a fitted line.
Scatter plot of species count against water temperature at 12 sites: counts fall as temperature rises, from about 22 species at 12 °C to 9 at 21 °C (r = −0.71).
Type, both variables, the direction and strength of the relationship and the range. If single points matter, for example an outlier, name them in the long description or give the values in a table.
Do this, not that
| Don't write | Write instead | Why |
|---|---|---|
| "Figure 2" | "Bar chart of mean exam scores by teaching method: …" | A placeholder tells the reader nothing[9]. |
| "Image of a graph showing the results" | "Bar chart of mean exam scores …" | Screen readers already announce a graphic. Name the chart type and the content[9]. |
| "The blue bar is the highest." | "The flipped classroom has the highest mean score, 71 points." | Colours that only separate groups mean nothing without sight. Name the groups. |
| "A huge improvement." | "9 points higher than lectures (71 vs 62)." | Readers asked for numbers, not adjectives[3]. |
| All 20 values in one sentence | The main values in the alt text, the rest in a table | A long alt text cannot be navigated; a table can[3]. |
| "Flipped classrooms are better." | "Mean scores were 71 points … and 62 points …" | Interpretation belongs in the discussion[4]. |
| The caption, copied | What the figure shows beyond the caption | The reader hears the caption anyway[6]. |
| "RT by cond. (ms)" | "Reaction time by condition, in milliseconds" | Abbreviations are spelled out letter by letter or mispronounced[8]. |
| "See figure." | "Details in Table 1 below the figure." | Point to something the reader can reach. |
Checklist for every figure
- The alt text names the figure type.
- It says what is measured or shown.
- It gives the main finding with numbers.
- It points to the long description or table, if there is one.
- It does not repeat the caption.
- It has no colours that only separate groups, and no interpretation.
- Abbreviations and symbols are written out.
- Every number matches your data.
- Decorative images are marked as decorative.
- After export, the PDF still contains your alt text.
Where to enter the text in Word, LaTeX, InDesign and other tools, and how to check the exported PDF, is explained in the complete guide.
The short version
- Pattern: figure type, what is measured, main finding with numbers, where the details are.
- One to three sentences in the alt text; everything else in a long description or a table.
- Describe what the figure shows. Significance comes from your analysis, meaning from your discussion.
- Name groups instead of colours, and numbers instead of adjectives.
- Check every number against your data and read the alt text aloud.
Sources
Checked in November 2026. Sources are marked as standard or law, research, or guidance from universities, publishers and specialist organisations.
- Standard / law W3C Web Accessibility Initiative. Understanding Success Criterion 1.1.1: Non-text Content (WCAG 2.2).
https://www.w3.org/WAI/WCAG22/Understanding/non-text-content.html - Standard / law W3C Web Accessibility Initiative. Technique G92: Providing long description for non-text content that serves the same purpose and presents the same information.
https://www.w3.org/WAI/WCAG22/Techniques/general/G92 - Research Jung, C., Mehta, S., Kulkarni, A., Zhao, Y. and Kim, Y.-S. Communicating Visualizations without Visuals: Investigation of Visualization Alternative Text for People with Visual Impairments. IEEE Transactions on Visualization and Computer Graphics 28(1), 2022 (IEEE VIS 2021).
https://arxiv.org/abs/2108.03657 - Research Lundgard, A. and Satyanarayan, A. Accessible Visualization via Natural Language Descriptions: A Four-Level Model of Semantic Content. IEEE Transactions on Visualization and Computer Graphics 28(1), 2022 (IEEE VIS 2021).
https://vis.mit.edu/pubs/vis-text-model.pdf - Guidance Elsevier. Journal Author Guide to Alt Text for Images. March 2026.
https://supportcontent.elsevier.com/Support%20Hub/Journals/Journal_Author_Guide_Alt_Text.pdf - Guidance Springer Nature. How to write good alt text.
https://www.springernature.com/gp/authors/publish-a-book/writing-your-manuscript/accessibility/how-to-write-good-alt-text - Guidance AIP Publishing. Alt text author instructions. 2026.
https://publishing.aip.org/wp-content/uploads/2026/03/Final_Alt-text_author_guidelines.pdf - Guidance DIAGRAM Center (Benetech). Image Description Guidelines: General Guidelines.
http://diagramcenter.org/?p=2097 - Guidance WebAIM (Utah State University). Alternative Text.
https://webaim.org/techniques/alttext/
Further reading
Write the alt texts, then send the file. DTP Services Berlin builds your descriptions, tables and formulas into a tagged PDF/UA file and tests it. For research projects in Germany, a science discount applies.
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