DEV3 AI Size Guide & Fit Advisor for WooCommerce

WooCommerce plugin for apparel stores: size charts with a cm/in switch and a phone bottom sheet, a "What size am I?" quiz built on measurement maths rather than AI, and return reasons that tell the quiz when a style runs small. Free download: sign in and click Download ZIP. Add your own Google AI Studio (Gemini) API key to switch on the AI features; the documentation says which features work without one.

How it works

We built DEV3 AI Size Guide & Fit Advisor as a WooCommerce plugin in PHP with a React admin and a small dependency-free storefront script. The size recommendation is deterministic; AI only helps with the work around it.

Key design decisions

• One data model, stored in base units. A chart holds one or more tables, columns of three kinds (size label, measurement, text such as US/UK/EU) and one row per size. Measurements are always stored in cm and kg; inches and pounds are converted on entry and on display, ranges at both ends.
• The quiz is maths, not AI. Fit\Engine scores every size row by how far each measurement falls outside its range, measured in that column's own step between sizes and weighted per measure. Fit preference adds ease to girths, a matching "usual size" is a strong signal, and missing chest, waist and hips can be estimated from height and weight with a lower weight and a lower confidence.
• Honest answers. Every result carries an alternative size when the shopper sits between two, a confidence level, a verdict per measure ("Waist: may be snug") and an out-of-range flag. A written explanation is built from the same facts; DEV3 AI can rephrase it, but only from those facts, and the template stays as the fallback.
• Returns move the quiz, but a person decides. Refund reasons, a Fit feedback box on orders (HPOS and legacy), manual records and a developer action feed a keyword classifier in five languages. When enough fit returns point one way, the merchant sees a "runs small" or "runs large" card and can shift the quiz by one size.
• A real phone sheet. Below 640 px the guide is a bottom sheet with swipe-to-close, a focus trap and safe-area padding, and tables scroll inside it with a sticky header row and size column.
• AI drafts, never auto-saves. The Google Gemini API can draft a chart from product data, a pasted table or a photo of a supplier chart, write the how-to-measure guide, classify unclear return notes and suggest category assignments. Each is a draft the merchant accepts.

Architecture

Charts are a private custom post type with JSON meta; a resolver picks the chart for a product by product override, then product, tag, category (including parents) and priority. Guide markup is rendered on the server, so it works before JavaScript loads and with full-page caches. Public quiz, explain and tracking endpoints are same-origin and rate-limited per IP. Return records and anonymous events live in two custom tables, with a unique key that makes refund imports idempotent. The API client, settings and usage logs come from a shared core used across DEV3's plugins.

What's in the download

• The installable plugin zip: upload it through Plugins → Add New → Upload Plugin.
• Full HTML documentation (installation, settings, hooks, FAQ).

Requirements

• WordPress 6.0 or newer and PHP 7.4 or newer
• WooCommerce 8.0 or newer, active (block and classic themes, HPOS and the cart/checkout blocks are supported)
• Optional: a Google Gemini API key for the AI chart drafts, the how-to-measure writer, return-note classification and friendly quiz explanations. Charts, templates, paste import, the "What size am I?" quiz and returns learning all work without one

Learn more

• How we built it: the AI Size Guide & Fit Advisor case study
• Engineering write-up on the DEV3 blog
• Also free in the DEV3 AI WooCommerce Plugins Bundle with every other WooCommerce plugin.