Alt text, short for alternative text, is a written description of an image on a webpage. It helps screen readers communicate visual information to people who cannot see an image and provides search engines with additional context about the image's content. Learning how to write effective alt text can improve website accessibility, support image SEO, and make web content more understandable.

For website owners, content writers, and SEO professionals, alt text should describe the meaningful information an image conveys rather than simply repeat keywords. The right approach depends on the image's purpose, the surrounding content, and the needs of the intended audience.

Alt text is an HTML attribute that provides a text alternative for an image. It is commonly added to an image using the alt attribute within an HTML <img> element.

For example:

<img src="eye-examination.jpg" alt="Ophthalmologist examining a patient's eyes">

In this example, the alt text describes the main action shown in the image. A screen reader can communicate this description to users who cannot see the visual content.

Alt text is different from an image filename, caption, or title attribute. A filename identifies the image file, while a caption is visible on the webpage. Alt text provides an alternative description when the image itself cannot be perceived.

Alt text supports several important aspects of website quality and search visibility.

1. Improves Website Accessibility

People who use screen readers rely on text alternatives to understand meaningful images. Descriptive alt text helps communicate information that would otherwise be available only visually.

For example, an image showing the steps of a website audit should describe the relevant action or information rather than use a vague description such as "SEO image."

2. Helps Search Engines Understand Images

Search engines use multiple signals to understand images, including the image itself, its surrounding text, its filename, and its alt attribute.

Descriptive alt text provides additional context about the subject of an image. This can help search engines interpret how the image relates to the webpage and its main topic.

3. Supports Image Search Visibility

Images can appear in Google Images and other visual search experiences. Accurate alt text can contribute to image understanding and discoverability.

However, adding alt text does not guarantee that an image will rank in search results. Image quality, page relevance, technical accessibility, and other signals also influence visibility.

4. Provides a Text Alternative When Images Fail to Load

If an image cannot be displayed, the browser may use its alternative text as a replacement, depending on the browser and context. This helps users understand the intended content even when the visual asset is unavailable.

Effective alt text should be accurate, concise, descriptive, and relevant to the image's purpose.

Start by identifying the main subject, action, or information conveyed by the image.

For example:

• Weak: alt="image1"
• Better: alt="Digital marketer reviewing website traffic analytics"
• Weak: alt="doctor"
• Better: alt="Ophthalmologist examining a patient's eyes with a slit lamp"

The better examples communicate specific visual information without unnecessary wording.

When an image is relevant to the page's primary topic, its alt text may naturally include a related keyword. However, the description should remain accurate even if the keyword is removed.

For example, on an article about technical SEO:

• Unnatural: alt="Technical SEO best technical SEO audit technical SEO services"
• Natural: alt="SEO specialist reviewing website crawl errors in an audit report"

The second example provides meaningful context without keyword stuffing.

There is no universal character limit for alt text. The appropriate length depends on the complexity of the image and the information a user needs.

Simple images may need only a few words. Charts, diagrams, and other information-rich visuals may require a longer description or an accompanying explanation in the page content.

Avoid adding unnecessary phrases such as "image of" or "picture of" when they do not improve clarity.

The same image may need different alt text depending on how it is used.

For example, a photograph of a laptop on a product page might need to identify the product model or relevant feature. On a blog about remote work, the same photograph might be described in terms of the activity it illustrates.

The description should reflect the image's purpose within the page, not just its appearance in isolation.

Not every image requires the same approach to alternative text.

• Image type
• Recommended approach
• Informative image

Describe the important information the image conveys.

Use an empty alt attribute: alt="".

Describe the product and relevant visible features.

Summarize its key message and provide detailed information in nearby text when necessary.

Describe the destination or action when the image functions as a link.

Include the essential text when it is necessary to understand the image's purpose.

Decorative images do not need descriptive alt text when they add no meaningful information. An empty alt attribute helps screen readers skip such images instead of announcing unnecessary details.

For complex charts and infographics, alt text alone may not communicate all the relevant information. Provide a fuller text explanation or accessible data table where appropriate.

Several common mistakes can reduce the usefulness of alternative text.

• Keyword stuffing: Repeating target keywords instead of describing the image.
• Generic descriptions: Using terms such as "photo," "image," or "graphic" without explaining the subject.
• Unnecessary length: Including irrelevant details that make the description difficult to understand.
• Misleading descriptions: Writing alt text that does not accurately represent the image.
• Duplicating nearby content: Repeating a complete caption when it adds no useful information.
• Leaving meaningful images undescribed: Using empty alt attributes for images that communicate important information.
• Adding alt text to every decorative image: Describing purely decorative visuals when an empty attribute would provide a better screen-reader experience.

A useful principle is to write alt text for the person who needs the information, not for a search engine crawler.

Website owners and SEO professionals can review image accessibility and optimization as part of a technical SEO audit.

Follow these steps:

1. Crawl important URLs: Use a website crawler such as Screaming Frog SEO Spider to identify images with missing alt attributes.

2. Review image context: Open the relevant pages and determine whether each image is informative, decorative, or functional.

3. Write meaningful descriptions: Describe each important image accurately and naturally.

4. Check for keyword stuffing: Remove repeated keywords and irrelevant promotional language.

5. Review implementation: Confirm that image elements contain appropriate alt attributes, including empty values for decorative images.

6. Recheck important pages: Verify that changes have been implemented correctly and that descriptions match the images.

Automated crawlers can identify missing attributes, but they cannot reliably determine whether every description is accurate or useful. Human review remains important.

• Alt text describes meaningful images for people who use screen readers and helps search engines understand image content.
• Write descriptions based on the image's purpose and the surrounding webpage context.
• Include relevant keywords only when they fit naturally into an accurate description.
• Use alt="" for purely decorative images that do not convey useful information.
• Provide additional text explanations for complex charts and infographics when needed.
• Audit alt attributes regularly, but evaluate descriptive quality through manual review.

Alt text is an important part of accessible web design and effective image SEO. It helps communicate visual information, provides context for search engines, and supports a better experience for users who cannot see images.

The best approach to writing alt text is straightforward: describe the meaningful content of the image accurately, keep the wording concise, and consider how the image supports the webpage's purpose. By applying these principles consistently, website owners can improve accessibility while supporting their broader SEO efforts.