LLM Image Descriptions: Best Practices for AI-Readable Alt Text
What separates an alt text an LLM cites from one it ignores. Templates and examples by image type.
Most alt text was written for screen readers and search engines. Both audiences are still primary, but a third has joined them: large language models like ChatGPT, Claude, and Perplexity that consume your images to answer their users' visual queries.
Writing for LLMs doesn't mean abandoning the principles that work for humans and Google — but it does mean leaning into specificity and structure more deliberately. Here's the playbook.
What LLMs Need from Alt Text
LLMs match queries to content via semantic similarity. When a user asks ChatGPT "find me a wool sweater under $80," ChatGPT scans candidate pages for textual content that matches the query semantically. Your alt text is part of that content.
The alt text that wins:
- Names the subject. "Wool sweater" beats "sweater."
- Lists relevant attributes. Color, material, size, brand, price tier.
- Reads as a coherent sentence. Not a comma-separated keyword list.
- Aligns with the surrounding paragraph. Misalignment looks suspicious.
Templates by Image Type
Product photo
Template: [Brand] [Product Name] in [color/material], [view angle], [distinguishing visual attributes].
Example: "Heather grey crew-neck cotton t-shirt with embroidered chest logo, flat lay, men's medium"
Editorial / hero image
Template: [Subject] [doing something], [setting], [visual mood].
Example: "Three coworkers reviewing a laptop screen at a sunlit conference table, warm afternoon light"
Chart / data visualization
Template: [Chart type]: [headline finding with specific numbers].
Example: "Bar chart: Product A revenue grew from $10K to $20K Jan-June; Product B steady at $12K; Product C declined from $15K to $8K"
Recipe / food photo
Template: [Dish] with [visible ingredients], [presentation style].
Example: "Bowl of cacio e pepe pasta with cracked black pepper and shaved pecorino, served on a white linen napkin"
Real estate / property photo
Template: [Room/area] with [specific features], [lighting], [notable details].
Example: "Master bedroom with king bed, white linens, exposed brick accent wall, morning light from south-facing window"
UI / software screenshot
Template: [Application] [view/screen] showing [specific UI element / state].
Example: "Shopify product editor with the AltText.ai panel showing auto-generated descriptions for 12 product images"
Patterns to Avoid
- Comma-separated keyword lists. "Blue, shirt, cotton, men, casual, summer" looks like SEO spam to both humans and LLMs.
- Marketing copy. "Premium, breathable, all-day comfort" tells the LLM nothing about what's actually visible.
- Stock-photo descriptions. "Successful businessperson at desk" is generic enough that an LLM can't differentiate your page from any other.
- Overstuffed alt text. Above ~140 characters, screen readers truncate and LLMs treat it as suspicious. Be specific but tight.
Multilingual Considerations
LLMs serve users in any language. If your alt text is English-only and your store sells internationally, non-English visual queries don't find you. AltText.ai generates alt text in 130+ languages — useful even for content sites that monetize via international AI search.
Testing AI-Readability
Three quick tests:
- Read the alt text out loud. Does it answer "what's in this image?" without context?
- Paste it into ChatGPT and ask: "what could this describe?" If the response is generic, your alt text is too.
- Search ChatGPT (with Browse) for queries the image should match. Check if your page is cited.
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