Once per 30 seconds. That's in our robots.txt: https://news.ycombinator.com/robots.txt. We've been working for a long time on (edit: what we expect to be) some serious performance improvements that might allow us to relax that limit. For now though, HN's process still runs on a single core and we don't have much performance to spare.

If you need more than that, you should use the Firebase-based API (https://github.com/HackerNews/API). The public dataset is also available as a Google BigQuery table: https://bigquery.cloud.google.com/dataset/bigquery-public-da....

Edit: since this subthread is not really on topic I detached it from https://news.ycombinator.com/item?id=21617478.