Bookworm

Updated 12 October 2026

A User-Agent like Verso/<version> (+https://verso.so/bookworm) is Bookworm, Verso’s feed fetcher, fetching a feed. Verso is an RSS reader from Mercer Street, in London. It hasn’t launched, so any request you see now is us testing.

To see how it’s doing against these rules, and how fresh posts are, see its status.

How often

• Requests are conditional. Verso sends back your ETag and Last-Modified, so an unchanged feed costs a 304 with no body.
• A feed is fetched at most every 30 minutes, or every 15 if it’s small and usually answers 304, and at least once a day.
• How often you publish doesn’t change the rate. <ttl> and sy:updatePeriod can slow it down, and skipHours and skipDays are respected.
• Each host gets one connection at a time and at most 72 requests an hour, across all its feeds. A short, reviewed list of very large hosts gets more.

Errors and redirects

• 429 and 503: it waits as long as Retry-After says, up to a week.
• Other errors: it waits about two hours, then twice as long after each error after that, up to a day.
• 410 Gone: it stops for good.
• 301 and 308: it switches to the new address.

Blocking it

Block or rate-limit User-Agents starting with Verso/. What follows the slash changes with each release, so match the prefix.

To ask us to slow down, drop a feed, or look at a problem, write to verso@mercer.st.