Catawiki is an auction site where every lot gets reviewed by a category expert who writes an estimated value range. That estimate is the single most useful number on the page, and it turns out Catawiki ships it to your browser in structured JSON, for every lot, before you even bid.
Compare the current bid against the expert estimate across a whole category and you have a shopping list of undervalued lots. I built a bot that does exactly that. Here is what I learned about the site on the way.
The data is in NEXT_DATA
Catawiki is a Next.js app, so each page embeds its state in a <script id="__NEXT_DATA__"> block. No hidden API, no reverse engineering, just parse the JSON out of the HTML.
Two levels matter:
