The alt tag, also known as the alt attribute or alternative text, is a central HTML-attribute that is integrated into website images to provide a textual description of the image content. Technically, it is part of the <img>-element in the HTML source code and is implemented as follows: <img src="bildname.jpg" alt="Description of the image content">.
Its primary function is to provide information about an image if it cannot be loaded or displayed for various reasons. This can be the case with a poor internet connection, defective image URLs or blocked image displays in the browser.
The importance of the alt tag for accessibility and SEO
The alt attribute fulfils two crucial functions in modern web design: it promotes digital accessibility and optimizes the Search engine friendliness (SEO) a website.
- Accessibility: The alt tag is essential for people with visual impairments or other visual limitations. Screen readers and other assistive technologies read out the alternative text to make the content of the image understandable. Since June 28, 2025 in Germany, for example, the Accessibility Reinforcement Act (BFSG) legal requirements that stipulate the barrier-free design of digital offerings, including the use of legacy texts, come into force.
- SEO optimization: Search engines like Google cannot „see“ or interpret images directly. The alt tag serves as a textual reference for the crawlers to understand the image content and classify it thematically. A meaningful alt text helps images to be found more easily in Google image search and can increase the relevance of the entire website for certain search queries. It is an important parameter of the On-page optimization.
Best practices for effective alt tags
The quality of an alt tag has a direct influence on its effect. The following points should be observed for optimal use:
- Precise and descriptive: The alt text should describe the visual content of the image briefly and precisely. Avoid general wording and be specific.
- Relevant Keywords integrate: Include relevant keywords in the alt text, of course, if they appropriately describe the image content and belong to the context of the page. Keyword stuffing, The excessive repetition of keywords should be avoided at all costs, as this can be evaluated negatively by search engines.
- Note the character limit: Although there is no hard technical limit, a length of around 125 characters, including spaces, is recommended to ensure that screen readers can read the text in full and search engines can process it optimally.
- No redundant phrases: Avoid phrases such as „image of“ or „photo of“, as screen readers already recognize this automatically.
- Empty alt attribute for decorative images: For purely decorative images that offer no added informational value, the alt attribute should remain empty (
alt=""). This signals screen readers to ignore the image and prevents unnecessary distraction for the user. - Individual alt tags: Each alt tag should be individually tailored to the respective image instead of repeating the main keyword of the page for all images.
The consistent and high-quality use of alt tags is a fundamental component of a comprehensive SEO strategy and contributes significantly to a barrier-free and user-friendly website.
