Which Parts of a Reading App Need the Internet

A reading app that needs a connection is a website. The reason to keep books as files on a device is that the device is the only thing you can rely on being there — on a plane, on the underground, on a mountain, or on the last day of a data plan.

Most of a reader works offline. A few specific things do not, and they are not the ones people expect.

Works with the network off

• Reading itself, in all six formats. The file is on the device; nothing is streamed.
• Reading position, bookmarks, highlights and notes. These live in the app’s own storage. They are also what makes backing up a library a two-part job, since copying the book files does not copy them.
• Fonts, themes, spacing, margins, brightness. All local rendering.
• Search inside a book, which reads the text already on the device.
• Importing files from storage.

That is the large majority of what a reader does, and it is worth being explicit: putting the phone in aeroplane mode does not degrade the reading experience.

Needs the network

Dictionary lookups. The definition is fetched from an online dictionary service rather than stored on the device. Offline, the panel fails. This is the one that surprises people, because “built-in dictionary” sounds local — and this one is neither local nor multilingual, as the article on in-book lookups sets out.

Browsing OPDS catalogues. Naturally: you are browsing a remote library. Books already downloaded from a catalogue read offline like any other file. What OPDS is covers the rest.

Cloud sync. Syncing progress between devices needs a connection to sync to. Reading continues offline; the sync happens when you are back.

Downloading text-to-speech voices. The speech itself runs on the device once a voice is installed, but Android downloads voices on demand. Install the voice you want before you need it, not on the plane.

The practical checklist before a flight

1. Import the books you want. Not “available in the cloud” — actually in the library.
2. Open each one for a moment. Some formats do parsing work on first open; better to find a broken file now than at 11,000 metres.
3. Install the speech voice if you plan to listen. This is the step people miss.
4. Accept that lookups will not work. If you are reading in a second language, this is the one to plan around.

Why this matters more than it used to

Reading apps have drifted toward requiring accounts and connections, partly for sync and partly because it is easier to build. The result is a category of app that stops working in exactly the situations where a book is most valuable.

Aurora Reader does not require an account to read local files, and the reading path does not touch the network. That is a deliberate constraint rather than a missing feature, and the cost of it is visible above: the dictionary and the catalogue browser are the places where the constraint was traded away, and both are honest about needing a connection rather than failing mysteriously.