books
Project Gutenberg (Gutendex)
The classic collection of around 75,000 free public-domain ebooks, with the Gutendex service exposing its catalogue as JSON for searching by title or author. You can also browse and download directly from the Gutenberg website. It is the go-to for complete, free ebook texts of out-of-copyright works, though the catalogue query can be slow or occasionally time out.
Why it’s useful & how it works
Project Gutenberg is the oldest and most established source of complete, freely downloadable public-domain ebooks, covering classic literature, historical texts, and early scientific works. You search by title or author on the Gutenberg website or via the Gutendex JSON catalogue, and can download in EPUB, Kindle, or plain-text formats with no account required. The collection focuses on works where US copyright has expired, so it is strongest for 19th-century and early 20th-century titles.
What’s inside
Approximately 78,000 free ebooks, primarily English-language but including works in dozens of languages, all in the public domain.
API access
https://gutendex.com/books?search= ... ; https://gutendex.com/books/ <id>
What we measured
Our own probes, not the archive’s own claims. Re-run periodically; every reading below is dated.
Reachability
- Direct request
- Responded HTTP 200 624 ms
- Through a datacenter proxy
- Responded HTTP 200 564 ms
- Gutendex API, direct
- Responded HTTP 200 119 ms
- Gutendex API, through a proxy
- Responded HTTP 200 2.3 s
- Gutendex page, direct
- Cloudflare challenge HTTP 200 156 ms (challenge-platform)
- Gutendex page, through a proxy
- Cloudflare challenge HTTP 200 556 ms (challenge-platform)
Did a real search return anything?
Returned results · 8 results for the sample query · median 881 ms · stable across runs
Works but slow (~6s); Gutendex occasionally times out, add retry/timeout tolerance.
Sample query: Frankenstein; or, the modern prometheus
Benchmark coverage
Found 5 of 8 test items (63%) in the Books cluster. Median response 4.5 s.
By how well known the item is: 2/3 well-known, 1/3 mid, 2/2 obscure .
One item it found: Frankenstein; or, the modern prometheus
Reachability measured 2026-08-22. Search checked 2026-08-22. Benchmark run 2026-08-22.
Access
Programmatic API access (a key may be required, see the API tag).