TL;DR: Alt text has no universal 125-character rule. It should be as short as possible and as long as necessary to replace the image’s purpose in context. Simple informative images often need one concise sentence. Functional images describe the action. Decorative images usually need empty alt text. Complex charts need a short label plus detailed information in nearby text.
Alt text length is often reduced to a number, but accessibility does not work that way. A ten-word description can be too long for a decorative image and far too short for a chart. The right text depends on why the image appears and what a person would miss without seeing it.
This guide explains how to write alt text for informative, functional, decorative and complex images. It also covers common mistakes, including keyword stuffing, repeated captions and descriptions that list visual details without communicating purpose. The aim is useful replacement text, not a perfect character score.
Draft the description in context, then check its size with the Character Counter. Counting is useful for spotting an overloaded description, but it should never force you to delete information that is needed to understand the page. The page context is therefore more important than any fixed count shown by a writing tool.
How Long Should Alt Text Be?
Alt text should be as short as possible and as long as necessary to communicate the image’s purpose. One concise sentence often works for a simple informative image. A functional icon may need only a few words. A complex chart usually needs a short alt attribute plus a longer explanation elsewhere.
There is no universal HTML or WCAG maximum of 125 characters. That number is a practical recommendation used by some teams and older tools, not a rule that makes longer text automatically inaccessible.
Read the page without the image and ask what information is missing. Write only that replacement. If the description becomes a paragraph, move the detail into visible body text so more people can use it.
What Should Alt Text Describe?
Describe the image’s purpose and the information it adds in this specific context. Do not list every visible object unless those details matter. The same photo may need different alt text on a news page, product page or personal profile.
The W3C requires non-text content to have a text alternative that serves an equivalent purpose, with exceptions for cases such as decoration. Its alt text decision tree helps choose between a description, functional label, nearby explanation or empty alt attribute.
Avoid starting with “image of” or “picture of” unless the medium itself matters. Screen readers and surrounding markup usually already identify the content as an image.
Informative, Functional and Decorative Images
Classify the image before writing. The classification decides whether the text should describe content, explain an action or remain empty.
- Informative image: communicate the fact or meaning the image adds. Example: “Red bicycle parked beside the station entrance.”
- Functional image: describe the action or destination. A magnifying-glass button needs “Search,” not “Magnifying glass.”
- Decorative image: use an empty alt attribute in HTML when the image adds no information and should be ignored.
- Image of text: include essential words if they are not already available as real text nearby.
- Logo: identify the organization when the logo provides that information. Inside a home link, the text may be “Company name home.”
Do not repeat a caption word for word. Repetition creates extra listening without adding meaning. Use the Text Difference tool to compare the caption and alt text when you suspect they are duplicates.
How Do You Write Alt Text for Charts and Complex Images?
Use a short alt attribute to identify the chart and its main message, then provide the important data, relationships or process in nearby text. Complex information rarely fits well inside one long alt attribute, and visible descriptions also help people with low vision or cognitive disabilities.
For a line chart, state the topic and key trend: “Monthly support requests rose from 120 in January to 210 in June.” Then add a data table or paragraph if exact monthly values matter.
For diagrams, describe the sequence or relationship that the page relies on. Do not describe every shape, arrow colour or position unless it changes the meaning. The readability checker can help you simplify a long visible description without removing essential steps.
Common Alt Text Mistakes
Bad alt text is often not too long or too short. It is irrelevant, repetitive or written for search engines instead of people.
- Using file names such as “IMG_2048.jpg.”
- Writing “image of” before every description.
- Repeating the caption, heading or nearby paragraph.
- Stuffing product keywords that the image does not communicate.
- Describing colour or position without explaining the meaning.
- Giving decorative images a spoken description.
- Using empty alt text for an image that is the only link or button label.
Clean copied descriptions with the extra spaces remover so stray line breaks and invisible formatting do not enter the CMS field.
How Do You Check Alt Text Before Publishing?
Review the image in its real page context. Decide its purpose, remove repeated information, test the page without the image and confirm that the replacement text supports the same task. Then inspect the final HTML or CMS output to ensure the attribute is present and correctly empty when decorative.
- Identify the image type: informative, functional, decorative, text-based or complex.
- Read the surrounding content: avoid repeating what is already available.
- Write the replacement: focus on purpose and useful information.
- Check length: shorten only when wording is redundant or overloaded.
- Review visual accessibility: use the contrast simulator when text or essential graphics appear inside the image.
- Test the output: confirm empty alt text is written as an empty attribute, not omitted.
Automated checkers can find missing attributes, but they cannot decide whether the words are useful. Human review is required because the correct description depends on context.
Alt text length is a quality decision, not a fixed SEO target. Simple images need concise replacement text, functional images need a clear action, decorative images should stay silent, and complex visuals need details outside the alt attribute. Finally, test the page with the image unavailable and confirm that the same information and action remain clear. That check is more useful than counting alone.
Draft the description beside the image, then use the Character Counter to spot unnecessary length. Keep every word that helps someone understand or use the page, and remove only the details that do not serve the image’s purpose.