Writing great alt text

Alt text is the short description a screen reader speaks in place of an image. Get it right and a photo carries its full meaning to blind and low-vision followers. Get it wrong — or skip it — and the image simply vanishes from their feed.

Start with the purpose, not the pixels

Before writing, ask: why did I post this image? Your alt text should carry that same meaning — no more, no less. A product photo, a meme, a chart and a decorative border all need very different descriptions, even if they're the same file size.

The purpose test: if the image disappeared and you had to replace it with a sentence, what would you write so the post still made sense? That sentence is your alt text.

Alt text vs. image descriptions

People use these terms loosely, but the distinction is useful:

  • Alt text goes in the platform's dedicated alt field. Make it as short as it can be while still conveying the image's purpose in context — a simple image needs only a few words, a busier one needs a sentence or two. Don't pad to hit a length, and don't repeat words already in the caption.
  • Image descriptions (ID) go in the visible caption or a comment, for when detail matters — art, complex infographics, or when identity is relevant. They can be longer and describe salient features: patterns, colours, setting, and the gender, race or disability identity of people when that's the point of the post.

Many creators do both: a tidy alt field, plus a richer "ID:" in the caption.

Write it well

  • Lead with what matters. "A man in a yellow raincoat runs through a rainy park" beats "a person outdoors".
  • Don't start with "image of…" or "photo of…". The screen reader already announces that it's an image.
  • Be specific, not exhaustive. Describe the meaning, not every leaf and cloud.
  • Don't keyword-stuff. Alt text is for humans, not SEO; cramming hashtags or repeated terms makes it painful to listen to.
  • No emoji in the alt field — their spoken names disrupt the description.
  • Match the tone. If it's a joke, the description can land the joke too.

Before: image of food
After: A plate of Maldivian mas huni — shredded tuna, coconut and onion — beside a warm roshi flatbread.

Text inside an image

If an image contains words — a quote card, a poster, a screenshot of a tweet — put all of that text in the alt or the caption. Otherwise it's invisible to screen-reader users and can't be searched, translated, or resized. Better still, post important text as real post text and keep the graphic for flavour.

Decorative images get empty alt

Not every image needs a description. A purely decorative divider, background texture or repeated brand flourish adds nothing to the message. On the web, give it alt="" so assistive tech skips it cleanly. The wrong move is to omit the attribute — that's when screen readers fall back to reading the filename.

Where the alt field lives, per platform

  • Instagram / Threads: Advanced settings → Write alt text before sharing. Overwrite any auto-generated text.
  • X (Twitter): enable image descriptions in settings, then tap +Alt on each image.
  • LinkedIn: click Alt text on each uploaded image.
  • Facebook: edit image → Alternative text → override the generated text.
  • Bluesky / Mastodon: an alt field on every image, with optional "missing alt" reminders — turn them on.
  • No alt field at all? Add a short image description in the post itself or the first comment.

Want the exact taps for each app, with character limits and the catches to watch for? See add alt text on every platform, step by step.

More examples to learn from

The same image gets a different description depending on why you posted it. Here are a few common cases, each shown weak then strong:

  • A portrait / selfie.
    ✕ me   ✓ Irshad, smiling, in a navy shirt against a whiteboard covered in wireframes.
  • A product shot.
    ✕ shoes   ✓ A pair of white running shoes with a teal sole, side on, laces tied.
  • A screenshot of a tweet.
    ✕ screenshot   ✓ Put the tweet's full text in the alt: Tweet from @a11ymv: "Captions aren't extra work — they're how most people watch."
  • A meme.
    ✕ funny meme   ✓ Describe the image and the joke: Two-panel drama meme: calm developer labelled 'ships without alt text', then panicking labelled 'sees the accessibility audit'.
  • A data chart.
    ✕ graph   ✓ Summarise the takeaway and put the numbers in the caption: Line chart showing support requests doubling from January to June 2024.

Notice the pattern: name the subject, the relevant detail, and — for anything with words or data — include the text itself.

A 30-second self-check

Turn on VoiceOver (⌘+F5 on Mac and iPhone) or Android TalkBack and let it read your post. If the image's meaning comes through with your eyes closed, your alt text is doing its job.

Alt text is one habit. See the rest — captions, hashtags, emoji and more — on the accessible social media guide.

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