Alt text length
There is no official character limit for alt text. There is a point where it stops helping. Type below and watch where yours lands.
73 characters · 13 words · ≈4.6 s to hear at a typical screen reader rate
A comfortable length for almost any image.
The listening time assumes about 170 words per minute, a common default; many screen reader users run faster.
Where "125 characters" comes from
You'll see 125 characters quoted as a hard limit. It isn't one. Neither the HTML standard nor WCAG sets a maximum, and current screen readers such as JAWS, NVDA and VoiceOver read long alt in full. The figure survives as a useful rule of thumb because long alt has a real cost: it is read in one go, and the listener can't skim, pause on a phrase or jump back a sentence the way they can in regular text.
What to do when it won't fit
- Cut what the page already says. If the heading names the product, alt needn't repeat the name and model number.
- Move detail into a caption. Everyone benefits, not just screen reader users.
- Use a long description for complex images: a data table, a paragraph below, or a
<details>element, as the W3C WAI complex images tutorial describes.
Social platform limits
| Platform | Alt text limit |
|---|---|
| X (Twitter) | 1,000 characters |
| Bluesky | 2,000 characters |
| Mastodon | 1,500 characters (server default) |
| Limit varies by app; keep it short | |
| No published limit; keep it concise |
Platform limits change; check each platform's help centre. For step-by-step instructions see how to add alt text.
Questions people ask
What is the alt text character limit?
There is no limit in HTML or WCAG. The common "125 characters" figure is a rule of thumb from older advice about some screen readers splitting long alt into chunks; modern screen readers read the whole alt, but long alt still cannot be paused or navigated, so shorter is kinder.
How long should alt text be?
Usually one sentence, often 5 to 20 words. Aim to say what the image contributes, then stop. If you need more than about 150 characters, move the extra detail into a caption or long description.
Can alt text be too short?
Yes. "Dog" or "chart" is too short when the image carries information. Length is a symptom; the real test is whether the alt conveys what a sighted visitor gets from the image in context.
What about alt text length on social media?
Platforms set their own limits: roughly 1,000 characters on X, 1,500 on Mastodon by default, and 2,000 on Bluesky; LinkedIn and Instagram vary by app. Instagram does not publish a fixed limit. Social alt can be longer because it is often the only description of the post.