Questions before you install

Short answers to the questions worth settling before you commit to running a server. For anything longer, each answer links to the page that goes deeper.

Do I need to run a server?

Q: Is there a hosted version of Tandem I can sign up for? No. Tandem is self-hosted — you run the server yourself, on your own hardware, holding your own files. There is no Tandem account and nothing you can subscribe to. See the home page.

Q: Can I try it without setting anything up? Yes. A public demo server holds a small set of public-domain books, already transcribed and synced, at demo.tandembook.com. It is read-only — you can read and listen, but not change the library — and it exists so you can see the sentence-level handoff working before you decide to install anything.

Q: What does it take to run my own server? Install the server walks through the whole thing: Docker Compose, a set of secret files, and a reverse proxy for TLS. It is not a one-click install.

What hardware?

Q: What does the server itself need? An x86-64 Linux host with Docker and Docker Compose. The server, Postgres and the web app run comfortably on ordinary hardware — no GPU is needed for the server process itself. Memory scales with the library: a server holding a few dozen books idles around 200 MB, and one holding about two thousand ebooks and audiobooks sits near 2.5 GB with Postgres using another 0.6 GB. Budget 4 GB for the stack on a large library, 2 GB for a small one, and cap the server container at that so a bad scan cannot take the host down. See Install the server.

Q: What actually does the transcription? Either a small GPU machine on your network — the reference setup is an NVIDIA Jetson Orin Nano — or local Whisper built into the server image itself, which runs on CPU if there is no GPU and is slow that way. The default medium model needs about 5 GB of memory while a job runs, GPU or unified; the Orin Nano's 8 GB with a swap file behind it is the reference, and a card with less than that wants the small model. Set up transcription covers both routes and how to choose.

Q: How long does transcribing a book take? There is no published number, because it depends on your hardware, the model size, and the length of the audiobook. Time your first real book on your own setup and extrapolate from there. Jobs run one at a time by design, so a queue of books finishes in sequence, not in parallel. See Set up transcription.

Q: Can I skip transcription and just use Tandem as a library? Yes. Without transcription set up you still get the library, the EPUB reader and the audio player — you just do not get the sentence-level handoff between them, since that depends on a transcript aligned to the book's text. See Set up transcription.

Books and formats

Q: Is there an iPhone app? No, and none is planned. The web app installs to the home screen as a Progressive Web App and behaves like a native app there, lock-screen controls included — that is the iPhone story. See Read and listen in sync.

Q: Which ebook and audiobook formats work? EPUB is the only ebook format that fully works: reading, and the sentence-level sync that depends on pulling text out of it. PDF can be paired with an audiobook but never aligns, since there is no extractable sentence text. MOBI and AZW3 files are recognized but have to be converted to EPUB first — Tandem can run that conversion itself. See Add your books.

Q: Does Tandem work with DRM-protected files? No — books need to be DRM-free. Bring files without DRM, or files you have already stripped it from yourself. See Add your books.

Q: My audiobook is a folder of numbered MP3 tracks. Will Tandem import it? Not as it is — an audiobook has to be a single file. Merge the tracks into one .m4b first (an audiobook manager's Merge to M4B tool is the easy route, and it can preserve chapter markers), then let Tandem scan the folder again. See Add your books.

Reading and listening

Q: How many people can use one server? As many as you invite. Tandem supports multiple accounts with roles, invite-only sign-up by default (open and closed modes are available too), and each person's reading position and bookmarks are their own. See Install the server.

Q: If I read on my phone and listen on my laptop, does my place carry over? Yes — that is the whole point. Position is written to the server as a chapter and a sentence within it, which both the web app and the Android app understand, so opening the same book anywhere shows the same place. See Read and listen in sync.

Privacy and cost

Q: What leaves my devices? Everything about your library, your reading and your account goes only to the server you point the app at — there is no Tandem company and no Tandem cloud collecting any of it. The one outside call the app makes on its own is the reader's Define action, which sends the single word you looked up to a dictionary service; nothing else leaves the device, and nothing is sent while you are simply reading or listening. Full detail: privacy policy.

Q: What does Tandem cost? Nothing. It is free, open-source software licensed under the AGPL-3.0. You pay for whatever hardware you choose to run it on, and nothing else. See the home page.