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Writing alt text with AI? Tell it what the image is for.

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Writing alt text with AI? Tell it what the image is for.
The plain request gets a description. With a plain request, GPT-5.5 gave a 168-character description of the mug, table and fern. It's a fine description, but it doesn't know where the image goes.

The plain request gets a description

Real output · GPT-5.5 (OpenAI API) · Oct 2026

Handmade speckled blue ceramic mug with a sand-colored base, steaming coffee, and handle facing right on a light oak table with a blurred potted fern in the background.

With a plain request, GPT-5.5 gave a 168-character description of the mug, table and fern. It's a fine description, but it doesn't know where the image goes.

Alt text depends on what the image does. W3C's alt decision tree asks what the image does, not what it shows. In a link, say where it goes. Adds meaning, describe it briefly. Decoration only, leave alt empty.

Alt text depends on what the image does

W3C's alt decision tree asks what the image does, not what it shows. In a link, say where it goes. Adds meaning, describe it briefly. Decoration only, leave alt empty.

Source: W3C WAI Images Tutorial, updated 13 May 2024

The move: say where it's used. Add one line about where the image sits. Our test gave the model a written description of a fictional photo instead of an uploaded image.

The move: say where it's used

Write alt text for this image. Where it is used: [where the image sits on the page, what clicking it does, and what text is already next to it]. Reply with the alt text only.

Tested in GPT-5.5 (OpenAI API), Oct 2026

Add one line about where the image sits. Our test gave the model a written description of a fictional photo instead of an uploaded image.

A linked thumbnail gets the product name. Told it was the only thing inside a link to the Harbor Mug page, it wrote 60 characters led by the product name. The fern, table and steam are gone.

A linked thumbnail gets the product name

Real output · GPT-5.5 (OpenAI API) · Oct 2026

Harbor Mug, speckled blue ceramic mug with sand-colored base

Told it was the only thing inside a link to the Harbor Mug page, it wrote 60 characters led by the product name. The fern, table and steam are gone.

Source: W3C WAI Images Tutorial, Functional Images

A mood banner gets empty alt. For a blog banner that never mentions the mug, it returned empty alt, which W3C says decorative images should have. In most site editors, leave the field blank or mark it decorative.

A mood banner gets empty alt

Real output · GPT-5.5 (OpenAI API) · Oct 2026

""

For a blog banner that never mentions the mug, it returned empty alt, which W3C says decorative images should have. In most site editors, leave the field blank or mark it decorative.

Source: W3C WAI Images Tutorial, Decorative Images, updated 27 July 2019

Context helps, but you still trim. In our test, with 'Speckled blue glaze' already printed next to the photo, it still wrote 156 characters. It repeated the glaze and kept the coffee and table. Trimming repeats is still your job.

Context helps, but you still trim

In our test, with 'Speckled blue glaze' already printed next to the photo, it still wrote 156 characters. It repeated the glaze and kept the coffee and table. Trimming repeats is still your job.

Write one line before you ask. Before you ask for alt text, write one line: where the image sits, what clicking it does, and what text is already next to it.

Write one line before you ask

Before you ask for alt text, write one line: where the image sits, what clicking it does, and what text is already next to it.

Try it: Run your next product photo twice, with and without that line.

Sources and assumptions

Assumptions:

The short version

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