Image Alt Text Best Practices
Alt text makes images accessible to screen-reader users and helps search engines understand your visuals. Here is how to write effective alt text for every type of image.
Alternative text (alt text) is a short written description of an image, read aloud by screen readers and shown when an image fails to load. Done well, it lets people with visual impairments understand your content and gives search engines the context they need to index your images. Done poorly — or left blank — it locks out users and wastes a ranking signal. This guide covers the WCAG-aligned rules, the three types of images you will meet, and exactly how to write alt text that works.
What Is Alt Text (and Why It Matters)
Alt text lives in the alt attribute of an HTML img tag. Screen readers announce it so blind and low-vision users know what an image shows. It is a core requirement of the Web Content Accessibility Guidelines (WCAG 1.1.1, Non-text Content), and in many regions it is a legal accessibility obligation.
Alt text does double duty for SEO. Google cannot see an image the way a person can, so it leans on the alt attribute, the surrounding text, and the file name to understand and rank the image — especially in Google Images. Clear, accurate alt text is one of the few places where accessibility and SEO pull in exactly the same direction.
The Three Types of Images
Before you write a single word, decide which kind of image you are describing. The right approach is completely different for each.
Decorative
Purely visual — borders, background flourishes, dividers. They add nothing to the meaning of the page. Give them an empty alt attribute so screen readers skip them. Never delete the attribute entirely.
alt="" (intentionally empty)Functional
Images that do something — a logo linking home, a magnifying-glass search button, a printer icon. Describe the action or destination, not the picture.
A search button → alt="Search"Informative
Images that carry information — photos, charts, diagrams, screenshots. Describe the information the image conveys. Complex visuals need a short alt plus a longer description nearby.
alt="Bar chart: 2025 revenue up 30% over 2024"How to Write Effective Alt Text
Lead with the point
Describe the main subject and what is happening, not how it looks. Put the most important information first.
Ex: "Golden retriever catching a frisbee in a park"
Keep it concise
Stay under about 125 characters. Screen readers do not pause inside alt text and many tools truncate longer strings. Push extra detail into a caption or long description.
Match the context
The right alt text depends on why the image is on the page. The same photo needs different alt text in a news article versus a camera-shop product listing.
Same image, different purpose → different alt
Skip the filler
Do not start with "Image of" or "Photo of" — screen readers already announce it as an image. Drop redundant words.
Bad: "Image of a red bicycle" → Good: "Red commuter bicycle"
Transcribe text in images
If an image contains text — a quote graphic, a sign, an infographic title — include that text word-for-word in the alt or nearby.
Poster reading "50% off" → alt must include "50% off"
Keywords, naturally
Include a relevant keyword once if it honestly describes the image. Never stuff keywords — it hurts both users and rankings.
Ex: "ai image describer dashboard"
Good vs. Bad Alt Text in Practice
The same image can have weak or strong alt text depending on context. Here is how to level up common cases:
| Image | ❌ Weak | ✅ Strong |
|---|---|---|
| Product photo (online store) | “shoes” | “Red running shoes, side view” |
| News article hero | “image1.jpg” | “Firefighters battling a wildfire near Athens” |
| Chart in a report | “graph” | “Line chart: active users doubled from Jan to June” |
| Decorative divider | “line” | “"" (empty — decorative)” |
Common Mistakes to Avoid
- Leaving alt missing entirely — screen readers may read the file name aloud instead.
- Writing "image", "photo", or "graphic" as the whole alt text.
- Keyword-stuffing the alt attribute to game search rankings.
- Describing a decorative image instead of giving it an empty alt.
- Duplicating the caption verbatim — alt and caption should complement, not repeat.
- Forgetting to transcribe meaningful text baked into an image.
Don't Forget File Names
Search engines read image file names too. A descriptive, hyphenated name reinforces the alt text.
IMG_3349.PNGred-running-shoes-side-view.pngWrite Alt Text Faster with AI
Describing every image by hand is slow. AI Image Describer reads your image and drafts a concise alt attribute, a longer description, and a caption in seconds — so you can follow the rules above without the manual grind. Always review the output for context and accuracy before publishing.
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Try the Alt Text GeneratorFrequently Asked Questions
What is image alt text?
Alt text is a short written description in the alt attribute of an HTML image tag. Screen readers read it aloud for visually impaired users, and it appears if the image fails to load. Search engines use it to understand the image.
How long should alt text be?
Aim for under about 125 characters. Most screen readers and tools handle that comfortably. If an image needs more explanation, keep the alt short and add a longer description in nearby text or a caption.
Do decorative images need alt text?
No. Decorative images that add no information should have an empty alt attribute (alt="") so screen readers skip them. Do not remove the attribute — leave it present but empty.
Is alt text a Google ranking factor?
Yes, indirectly. Google uses alt text to understand images, which helps them rank in Google Images and adds context to the page. But write it for users first — keyword-stuffing can hurt more than help.
Should I include keywords in alt text?
Include a relevant keyword only if it describes the image accurately, and only once. Accurate description always comes before keywords; stuffing harms both accessibility and SEO.