Discover a Webflow site's CMS collections and read a collection's field schema before writing items

Documented steps

1. GET https://api.webflow.com/v2/sites/{site_id}/collections (scope cms:read) returns { collections: [...] } with id, displayName, singularName, slug, createdOn, lastUpdated.
2. Match the collection you want by slug rather than displayName — display names are edited freely by designers, slugs are stable.
3. GET https://api.webflow.com/v2/collections/{collection_id} (scope cms:read) returns the collection with a fields[] array.
4. Each field carries id, displayName, slug, type (PlainText, RichText, Image, MultiImage, VideoLink, Link, Email, Phone, Number, DateTime, Switch, Color, Option, File, Reference, MultiReference, User), isRequired, isEditable and a type-specific validations object.
5. Build your write payload keyed by each field's slug — fieldData on items is keyed by field slug, not by displayName or field id.
6. Cache the schema per collection and re-fetch when a write fails validation, rather than re-fetching on every item.