AI Auto Alt Text Generator

AI Auto Alt Text Generator is a lightweight, privacy-conscious plugin that uses OpenAI vision-capable models (defaulting to GPT-5.4 nano, with GPT-5.4 mini and legacy GPT-4o mini options) to create meaningful, screen-reader-friendly alt text and SEO-friendly titles for your images. Whether you add a single image, bulk-process your library, or just want a one-click fix in the Media Library, the plugin handles it all – no manual effort required.

This solution is far cheaper than many alternatives because it cuts out the middle-person. You’ll just need to bring your own OpenAI API key.

✨ Key features

• Automatic alt text on upload – set-and-forget accessibility.
• Optional automatic image titles – improve SEO with descriptive titles.
• One-click manual generation – “Generate Alt Text & Title” button in the Media Library.
• Bulk update tool – batch-process existing images, including those that only have filename-based alt text, with a configurable pause between batches.
• Prompt fine-tuning – supply site-wide context and optionally include the image file name.
• Model selection – default to GPT-5.4 nano (fastest & cheapest) or switch to GPT-5.4 mini for higher quality; legacy GPT-4o mini and GPT-5 mini/nano remain available.
• Image size & detail control – choose the resolution and level of visual detail sent.
• Developer-friendly – filters and actions to customise prompts, models and output, plus optional outgoing webhooks.
• WordPress Abilities API – registers a generate-alt-text ability (WordPress 6.9+/7.0) so core AI, agents and automation tools can generate alt text.
• No extra servers – data flows only between your site and OpenAI; nothing is stored off-site.
• Multilingual output – choose English (UK), English (US) or other popular languages. (English US is the default.)

🧭 Where to find the bulk tool

• Tools → Bulk Alt Text Update
• Media → Bulk Alt Text Update (shortcut that redirects to the Tools page)
• Settings → Alt Text Generator includes a button linking straight to the bulk page

🧠 How it works

1. When an image is uploaded (or manually chosen), the plugin creates a temporary public URL for that image.
2. It sends the image – plus optional context such as the parent post title, your custom site context and the file name – to your selected OpenAI vision model.
3. OpenAI returns a concise description.
   • Alt text is stored in WordPress’ native _wp_attachment_image_alt field.
   • (Optional) The returned title is stored as the attachment post title.
4. Nothing is cached or stored on OpenAI’s side; only the final strings live in your database.

Settings overview

• OpenAI API Key – Required to connect to OpenAI.
• OpenAI Model – GPT-5.4 nano (default), GPT-5.4 mini, or legacy GPT-4o mini / GPT-5 mini / GPT-5 nano.
• Image Size to Send – Thumbnail, Medium, Large, or Full.
• Image Detail Quality – ‘Low’ or ‘High’ (Low uses fewer tokens).
• Bulk batch size – Number of images per batch (lower values reduce rate-limit risk).
• Site Context – Optional free-form prompt guidance (brand voice, niche, etc.).
• Send Image File Name – Include file name in the prompt for extra context.
• Automatically Generate Title – Add descriptive titles alongside alt text.
• Use full context for image titles – When enabled, title generation includes site context and file name (uses more tokens).
• Bulk optimiser delay (seconds) – Pause between batches during bulk runs.
• OpenAI request timeout (seconds) – Max wait time for OpenAI responses (10–120s) to reduce timeout failures on slower hosts.
• Output Language – Default English (US). Choose English (UK) for British spellings or another popular language; outputs (alt text and titles) will be generated in the selected language.
• Webhook URL & signing secret – Optionally POST generated alt text/titles to an external endpoint (with an optional HMAC-SHA256 signature) for automation and logging.

Developers

The plugin is extensible via standard WordPress hooks, an outgoing webhook, and the WordPress Abilities API.

Filters

• aatg_alt_text_prompt ( $prompt, $post_ID, $context ) – customise the alt-text prompt.
• aatg_image_title_prompt ( $prompt, $post_ID, $context ) – customise the title prompt.
• aatg_openai_request_payload ( $payload, $context, $messages ) – customise the full OpenAI request (model, messages, reasoning effort).
• aatg_generated_alt_text ( $alt_text, $post_ID ) – filter alt text before it is saved.
• aatg_generated_title ( $title, $post_ID ) – filter the title before it is saved.
• aatg_is_low_quality_alt ( $is_low, $alt, $post_ID ) – control which existing alt text the bulk tool regenerates.
• aatg_webhook_payload ( $payload, $post_ID, $result ) – customise the outgoing webhook body.
• aatg_supported_image_extensions ( $extensions ) – customise which image formats are sent to OpenAI (default: PNG, JPEG, GIF, WebP).

Actions

• aatg_after_alt_text_generated ( $post_ID, $alt_text )
• aatg_after_title_generated ( $post_ID, $title )
• aatg_after_generation ( $post_ID, $result )

Outgoing webhook

Set a Webhook URL under Settings → Integrations & Webhooks to receive a non-blocking JSON POST after each generation. If a signing secret is set, requests include an X-AATG-Signature: sha256=… header (HMAC-SHA256 of the body) so your endpoint can verify authenticity.

WordPress Abilities API

On WordPress 6.9+ the plugin registers the ability ai-auto-alt-text/generate-alt-text (input: attachment_id) so WordPress core AI, agents, MCP servers and automation tools can generate alt text programmatically. Execute it with wp_get_ability( 'ai-auto-alt-text/generate-alt-text' )->execute( array( 'attachment_id' => 123 ) ).

External services

This plugin connects to the OpenAI API to generate alt text and (optionally) image titles.

• Endpoint: https://api.openai.com/v1/chat/completions
• When called:
  • On image upload (automatic)
  • Via “Generate Alt Text & Title” button in Media Library (manual)
  • Via Tools → Bulk Alt Text Update (bulk)
• Data sent: image URL, optional file name, optional site context, optional parent post title
• Terms: https://openai.com/policies/terms-of-use
• Privacy: https://openai.com/policies/privacy-policy

If you configure a Webhook URL, generated alt text/titles (and the image URL) are also sent to that endpoint you control.