What is OPDS?

In one line: OPDS (Open Publication Distribution System) is a catalogue feed for books. A server publishes a list of books at a web address; your reading app reads that address and lets you browse, search and download without leaving the app.

Why it exists

The normal way to get a book onto a phone is tedious: open a browser, find the download link, hope the file lands somewhere findable, then import it. Multiply by every book and it becomes the reason people give up on free libraries and just buy from a shop instead.

OPDS removes those steps. The catalogue appears inside the reader, like a shop that lives in the app but is run by whoever published the feed: a library, a public-domain archive, or a server in your own house.

How it works, briefly

An OPDS catalogue is a plain web feed, closely related to Atom and RSS. It lists entries with a title, author, description, cover and one or more download links. Reading apps understand that structure, so they can render it as a browsable catalogue with search.

There are two generations in use: OPDS 1.x, based on Atom XML, which nearly everything supports, and OPDS 2.0, based on JSON, which is newer and cleaner. As a reader you don’t need to care which one a catalogue uses.

Because it’s an open feed, nothing about it locks you in. The books you download are ordinary files that stay yours after the catalogue disappears.

Who publishes an OPDS catalogue

• Project Gutenberg, with tens of thousands of public-domain books.
• Standard Ebooks, which republishes public-domain works with careful modern typography.
• The Internet Archive and various national and university libraries.
• Your own server. Calibre-Web, Kavita and Komga all expose your collection as an OPDS feed, which turns a home server into a private bookshop for your phone.
• Some public library systems, though borrowing usually still goes through their own DRM-bound app.

Adding a catalogue

The whole process is: find the catalogue URL, paste it into your reader, done. Most apps that support OPDS ship with a few catalogues already configured so you can see what it looks like before adding your own.

Lectern comes with Project Gutenberg and Standard Ebooks built in, accepts custom catalogue URLs, and can also sync with a Calibre-Web server if you run one. Browsing, downloading and reading all happen in one place, and downloaded books join your normal library like any other file.

Two practical cautions

1. Only add catalogues you trust. An OPDS feed is just a web address, and it can serve any file it likes. Stick to known projects and servers you control.
2. Catalogues are not backups. If a book matters to you, keep the downloaded file in your own folder rather than assuming the feed will still be there next year. See organising a digital library.

If you have ever wanted a bookshop that isn’t a shop, OPDS is the closest thing the open web built.

Frequently asked