Design5 min read
Instagram Alt Text: Where the Field Is, and What to Put in It
Instagram writes an automatic description for every image whether you do or not. Yours replaces it, you get 100 characters, and the field is three taps deep.
Instagram alt text lives under Advanced settings → Write alt text on the last screen before you post, and it holds 100 characters. If you leave it empty Instagram generates its own description from object recognition; what you write replaces that, it does not add to it.
Where the field is
On a new post, the field is at the end of the flow rather than beside the image, which is why most people have never seen it.
- Pick the image and continue to the final screen — the one with the caption box.
- Scroll to the bottom and open Advanced settings.
- Tap Write alt text.
- Type the description and go back. It saves with the post.
On a post that is already live:
- Open the post, tap the … menu, and choose Edit.
- Tap Edit alt text in the corner of the image.
- Save.
For a carousel, the field is per image. Editing one slide does not touch the others, and this is the most common place alt text goes missing — the first slide gets a description and the other nine do not.
Instagram documents the field and its automatic alternative text in its own help centre (Instagram Help).
What Instagram writes if you do not
Instagram generates a description automatically using object recognition. It is generic by design: it names objects it recognises with reasonable confidence and stops.
That produces descriptions along the lines of "May be an image of one person, food and indoor" — technically true, and useless for deciding whether to care about the post. It also cannot know what the picture is for, which is the only thing your description needs to carry.
Writing your own is the entire fix, and it takes one sentence.
The 100 characters, and what fits in them
A hundred characters is about fifteen words. That is one clear sentence, which is the right size for most photographs.
It is not enough for two things, and both are worth knowing before you design the image:
- A quote card or an infographic. Every word in the graphic has to be in the alt text,
because for a listener that text is the image. On Instagram this is frequently impossible, which is a genuine argument for putting the key line in the caption too.
- A chart. The trend and the numbers do not fit either.
Every network's limit is different, and Instagram's is the tightest of the group — the full table is in alt text character limits.
FreeMentioned in this article
Alt Text CheckerReads your image description the way a screen reader will.It checks the length against Instagram's field, shows where an over-long description would be cut, and runs the rules below.
Four things that make Instagram alt text useless
Starting with "image of". The screen reader announces that it is an image before it reads a word of your text, so the listener hears "image, image of a loaf". Start with the subject.
Pasting in the caption. A listener then gets the same sentence twice and still does not know what is in the picture. The caption says what you think; the alt text says what is there.
Hashtags. Alt text is not searched on Instagram, so a tag reaches nobody. What it does is get read aloud as "number sign" or as one run-on word, in the middle of a description of a photograph. Every platform's accessibility guidance names keyword stuffing in this field specifically.
Nothing at all on a carousel's other slides. See above. This is a per-image field.
A format that works
Subject, then what it is doing, then the detail that made you post it. One sentence, no preamble:
A sourdough loaf split open on a wooden board, the crumb wide and irregular.
Seventy-five characters, no "image of", nothing from the caption, and a listener now knows exactly what they are being shown and why it is worth a post.
The general version of the rules — and the reason the field exists at all — is in social media alt text. The other thing on an Instagram post that is read aloud one item at a time is the emoji, which is covered in too many emoji.
Where is alt text on Instagram?
On the final screen before you post, under Advanced settings → Write alt text. On an existing post it is under Edit → Edit alt text on the image itself.
How many characters is Instagram alt text?
100. It is the tightest alt text field of any major network.
Does Instagram alt text help SEO?
No. Instagram does not index alt text for search, and hashtags in the field reach nobody. It is read by screen readers, and that is the whole audience.
Can I add alt text after posting?
Yes. Open the post, tap the … menu, choose Edit, then Edit alt text on the image. On a carousel you have to do it per slide.
Write the sentence, then paste it into the alt text checker with Instagram selected — the 100-character field is easier to overrun than it looks.
Put it to work
Tools for the job you just read about
Free to run, most of them without an account.
FreeContent
Alt Text Checker
Reads your image description the way a screen reader will.
Check →1 runs
FreeContent
Keyword Density Checker
How often the phrase appears, and — the part that matters — how early.
Check →1 runs
FreePreviews
Google SERP Snippet Preview
See your title and description as a Google result — on a desktop and a phone.
Preview →5 runs
FreeUtilities
Social Media URL Cleaner
Strip the tracking off a link — and see what each parameter was telling somebody.
Clean →1 runs
FreeAnalytics & growth
Instagram Money Calculator
What to charge for a post — priced the way a brand actually prices it.
Calculate →
FreeContent
Caption Line Break Generator
Paragraph breaks that survive the paste into Instagram.
Generate →1 runs
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