Last updated: March 2026
Why Image Descriptions Matter for Accessibility
Over 2.2 billion people worldwide have some form of vision impairment, according to the World Health Organization. For these users, alt text is the only way to understand images on the web. Screen readers rely on alt text to describe images aloud, making it an essential component of web accessibility.
The Web Content Accessibility Guidelines (WCAG) 2.1 require that all non-decorative images include meaningful alternative text. Failure to provide alt text not only excludes users with disabilities but can also result in legal liability under the ADA and similar accessibility laws in other countries.
How This Tool Works
Browser-based image analysis. When you upload an image, the tool uses the HTML5 Canvas API to extract visual features directly in your browser. It identifies the top 5 dominant colors, measures overall brightness and contrast levels, calculates edge density (which indicates detail and sharpness), and records the image dimensions and aspect ratio.
AI-powered description generation. The analysis results, along with the image itself, are sent to Claude AI, which generates three levels of description. The alt text follows WCAG best practices at 125 characters or fewer. The short description provides a 2-3 sentence summary. The detailed description offers a comprehensive 4-6 sentence account of the image including colors, composition, and mood.
Ready-to-use HTML output. The tool also generates an HTML code snippet with the alt text already embedded, so you can copy and paste it directly into your website or application.
Best Practices for Alt Text
Be concise and specific. Good alt text describes the image in under 125 characters. Avoid starting with "Image of" or "Picture of" since screen readers already announce the element as an image. Focus on the most important information the image conveys.
Consider the context. The same image may need different alt text depending on where it appears. A photo of a person might need their name on an about page but a description of their action on a news article. Always review and customize the generated descriptions for your specific use case.
Use empty alt text for decorative images. If an image is purely decorative and adds no informational value, use an empty alt attribute (alt="") to tell screen readers to skip it. This prevents unnecessary noise for visually impaired users.
Avoid redundancy. Do not repeat information that is already present in surrounding text. If a caption describes the image, the alt text should complement it rather than duplicate it.
Frequently Asked Questions
How does the AI image describer work?
The tool analyzes your image in two stages. First, it performs pixel-level analysis in your browser to extract dominant colors, brightness, contrast, edge density, and dimensions. Then it sends this analysis along with the image to Claude AI, which generates three descriptions: a concise alt text (under 125 characters), a short 2-3 sentence description, and a detailed 4-6 sentence description.
Is my image data kept private?
Yes. The canvas-based pixel analysis runs entirely in your browser. The image and analysis summary are sent directly to the Anthropic API using your own API key — our servers never see your images. No images or descriptions are stored anywhere after generation.
What is alt text and why does it matter?
Alt text (alternative text) is a text description added to images in HTML. It is read aloud by screen readers for visually impaired users, displayed when images fail to load, and used by search engines to understand image content. WCAG accessibility guidelines require meaningful alt text on all non-decorative images. Good alt text should be concise (under 125 characters), descriptive, and convey the purpose of the image.
Do I need an API key to use this tool?
Yes, you need an Anthropic API key to generate AI descriptions. You can get one at console.anthropic.com. The key is stored only in your browser's localStorage and sent directly to Anthropic's API — it never touches our servers. Each API call costs a fraction of a cent.