Generate WordPress Image Alt Text with OpenAI Vision (n8n)

Automatically generate missing WordPress image alt text using OpenAI Vision (in n8n)

This n8n workflow finds WordPress media library images that are missing alt text, generates concise, language-specific descriptions with the OpenAI Chat Completions API using vision, validates the output, and (optionally) writes the alt_text back to WordPress via the REST API.

What this workflow does

• Runs manually or on a schedule: it can be triggered by you, or run every Monday at 9am.
• Fetches recent WordPress media: pulls image attachments from the WordPress REST API media endpoint.
• Filters for missing alt text: selects images that have no existing alt text and limits processing to supported formats (JPEG/PNG/WebP).
• Chooses an image URL: selects a suitable image URL for each media item.
• Generates alt text with OpenAI Vision: sends the image URL (and optional title context) to OpenAI, using the configured language and maximum length.
• Validates and normalizes results: parses and validates JSON output, removes “Image of…”-style prefixes, enforces maxAltLength, and marks items as ready or skipped.
• Optional write-back: with dry run enabled it outputs proposed alt text; otherwise it updates the media item’s alt_text in WordPress.

Use cases

• Maintain SEO accessibility across a growing WordPress media library by auto-filling missing alt attributes.
• Run a weekly compliance sweep for SaaS or agency sites to reduce manual content cleanup.
• Use dry run first to review suggested alt text before updating WordPress.

Technical details

• WordPress REST API with HTTP Basic Auth using a WordPress Application Password.
• OpenAI Chat Completions API with vision (configurable model, language, limits, and maxAltLength).
• n8n nodes used: manual trigger, if, set, code, sticky note, and HTTP Request.