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generate_alt_text ​

Generate descriptive alt text for images to improve accessibility. Provide either an image URL or base64 encoded image data. Optionally include context about the image.

Authentication ​

Optional - This tool works without authentication.

Parameters ​

ParameterTypeRequiredDefaultDescription
imageUrlstringNo*-URL of the image to analyze. Must be a valid URL.
imageDatastringNo*-Base64 encoded image data.
contextstringNo-Optional context about the image to improve description quality.
maxLengthnumberNo200Maximum length of generated alt text. Must be between 10 and 1000.

*Either imageUrl or imageData must be provided.

Response ​

typescript
{
  success: boolean;
  altText: string;
  suggestions: string[];
  guidelines: {
    dos: string[];
    donts: string[];
  };
}

Examples ​

Generate Alt Text from URL ​

json
{
  "imageUrl": "https://example.com/image.jpg",
  "maxLength": 200
}

Generate Alt Text with Context ​

json
{
  "imageUrl": "https://example.com/chart.png",
  "context": "This is a bar chart showing quarterly sales data for 2024",
  "maxLength": 250
}

Generate Alt Text from Base64 Data ​

json
{
  "imageData": "data:image/jpeg;base64,/9j/4AAQSkZJRg...",
  "maxLength": 150
}

Error Handling ​

Common errors:

  • InvalidRequest: Neither imageUrl nor imageData provided, or invalid parameters
  • InvalidUrl: imageUrl is not a valid URL
  • InvalidImageData: imageData is not valid base64 encoded data
  • ImageTooLarge: Image exceeds maximum size limit

Best Practices ​

  1. Provide Context: Include context parameter for more accurate descriptions
  2. Appropriate Length: Use 100-200 characters for most images
  3. Be Specific: Generated text should be specific and descriptive
  4. Review Output: Always review and edit generated alt text
  5. Include Text: If image contains text, ensure it's in the alt text
  6. Avoid Redundancy: Don't start with "image of" or "picture of"
  7. Test with Screen Readers: Verify alt text works well with assistive technology

Alt Text Guidelines ​

Do: ​

  • Describe the content and function of the image
  • Be accurate and specific
  • Keep it concise (under 125 characters when possible)
  • Include important text that appears in the image
  • Describe the mood or emotion if relevant
  • Use proper punctuation and grammar

Don't: ​

  • Don't start with "image of" or "picture of"
  • Don't include redundant information
  • Don't use overly technical jargon unless necessary
  • Don't describe decorative images (use empty alt instead)
  • Don't make assumptions about what's not visible
  • Don't exceed the character limit unnecessarily

Alt Text Examples ​

Good Alt Text: ​

  • "Golden retriever puppy playing with a red ball in a grassy park"
  • "Bar chart showing 25% increase in sales from Q1 to Q4 2024"
  • "Woman in blue dress speaking at podium with microphone"

Poor Alt Text: ​

  • "Image of a dog" (too vague)
  • "Picture of a chart" (not descriptive)
  • "IMG_1234.jpg" (filename, not description)

Special Cases ​

Decorative Images ​

For purely decorative images, use empty alt text:

json
{ "altText": "" }

Complex Images ​

For charts, diagrams, or infographics:

  • Provide a concise summary in alt text
  • Consider adding a longer description in the post text
  • Include key data points and trends

Text in Images ​

If the image contains text:

  • Include all important text in the alt text
  • Maintain the order and structure of the text
  • Consider using OCR for accuracy

Implementation Note ​

This is a placeholder implementation that provides guidance on writing good alt text. In a production environment, this would integrate with a vision AI service (like GPT-4 Vision, Claude Vision, or Google Cloud Vision API) to automatically analyze images and generate descriptions.

Rate Limiting ​

This tool is not subject to AT Protocol API rate limits as it performs local analysis.

See Also ​