Developer reverse-engineers Google's undocumented API to extract iframe data

A developer spent two days extracting flashcard data from Google's NotebookLM, which renders content inside a cross-origin iframe. By intercepting the network request to Google's internal batchexecute endpoint, they parsed a 1.5MB response to find clean JSON. The solution required injecting a script into the page's main world to hook XHR calls, bypassing the same-origin policy.