Guidelines for Writing Effective Image Alt Text

Effective alt text is essential for accessibility, user experience, and SEO. It enables screen readers to describe images to visually impaired users and helps search engines index images for relevant content. Follow these technical guidelines to write precise and accessible alt text for your images.

1. Convey Only Necessary Context

An image's alt text should convey only the essential information. If the image supports or enhances the content, describe it briefly but clearly. Alt text should be contextual, meaning that it reflects the purpose of the image within its specific use case:

• Example: For an image of a sunset used in an article about summer vacations, “Sunset over a beach with palm trees” provides relevant context. However, a more general description like “Beautiful sunset” lacks specific value.

Avoid overloading the alt text with superfluous details, as this can confuse users and clutter the interface for screen readers. Limit descriptions to concise, relevant details that help users understand the image’s purpose.

2. Describe Important Visual Elements

Identify critical elements in the image and describe them in a logical order, typically foreground to background. This approach is especially useful in complex images or when an image has multiple objects that contribute to its overall message.

• Example: For an image showing a person typing code on a laptop, “Person typing HTML code on a laptop” captures the essence without unnecessary details.

Use specific terms for items in the image. Instead of general terms like "thing," "object," or "stuff," specify what the objects are if it adds value to the image's purpose in the content.

3. Avoid Repeating Contextual Information

If surrounding content or image captions provide context, avoid redundant alt text. Alt text should add unique value, so eliminate any content that is implied or already stated:

• Example: For a labeled bar chart image showing monthly sales data, “Bar chart depicting monthly sales data” is redundant. Instead, simply describe what the data represents, such as “Monthly sales trend, with peak in August.”

Similarly, avoid repeating the same information if the context (such as the section heading or caption) already describes it.

4. Use Active Descriptions

Whenever possible, describe images in an active voice, making descriptions more dynamic and engaging. Active descriptions can better convey movement or interactions within the image:

• Example: Instead of “Laptop with code displayed on screen,” use “Laptop displaying HTML code on screen.”

Active descriptions help clarify what the image represents, especially when users rely on screen readers.

5. Omit Words Indicating an Image

Do not begin alt text with phrases such as "Image of" or "Picture of." These phrases add no new information since screen readers already indicate the presence of an image to users.

• Example: Instead of “Image of an orange cat playing with a ball toy,” use “Orange cat playing with a ball toy.”

Simply describe the image contents directly. This approach keeps alt text short and focused on what matters.

6. Handle Decorative Images with Empty Alt Text

If an image is purely decorative and does not add value to the content, assign it an empty alt attribute (alt=""). This tells screen readers to skip the image, reducing clutter for users who rely on assistive technology.

For example, images used solely for layout purposes or visual styling do not need alt text. Assigning empty alt attributes in these cases enhances usability by allowing users to bypass unnecessary content.

7. Incorporate Relevant Keywords for SEO

When writing alt text, incorporate relevant keywords naturally, as this can improve SEO for images without compromising accessibility. Place keywords in the alt text only if they directly relate to the image content. Forced keywords or keyword stuffing will degrade the quality of alt text for accessibility users.

• Example: For an article on “home automation,” an image showing a smart thermostat can use alt text like “Smart thermostat settings for home automation.” Avoid forced repetition of keywords that would detract from readability.

Keywords should add descriptive value without making the text sound artificial or forced.

8. Limit Alt Text to 125 Characters

Limit alt text length to 125 characters, as many screen readers truncate longer descriptions. If an image requires more detail, consider placing a longer description in the surrounding text if applicable.

Character limits encourage brevity, which is critical for users who rely on quick, concise descriptions. Longer descriptions can disrupt content flow and slow down the reading experience.

9. Use Punctuation for Readability

Punctuation in alt text can significantly enhance readability for screen readers. Proper punctuation allows screen readers to pause, making the text easier to understand.

• Example: For an image of a city skyline at sunset with a rainbow, “City skyline at sunset, rainbow visible over the skyscrapers” reads more naturally than an unpunctuated alternative.

Punctuation can aid in separating ideas or descriptive elements, especially in alt text that describes multiple parts of a complex image.

10. Avoid Using Alt Text for Complex Images or Infographics

For complex images or infographics, alt text may not fully describe the content. In these cases, use a surrounding text explanation to provide a comprehensive description.

• Example: For an infographic on climate change data, a simple alt text might be “Infographic on climate change data,” with a longer text or tabular data explanation nearby detailing key points. This approach prevents cluttering alt text with excessive detail while still providing access to the full information.

In complex cases, clear, accessible descriptions outside of the alt attribute can support users better than overextended alt text.

By adhering to these guidelines, you can create effective alt text that supports both accessibility and SEO goals. These practices enhance usability for screen reader users and optimize images for search engines, contributing to a more inclusive web experience.