Privacy · 7 min read

By Mohamad Mohamad · 4 August 2026

Do reading apps track what you read?

Mostly yes — though "tracking" covers several different things, only some of which are sinister, and the one people worry about least is the one that gives away the most.

Four things that leave your phone

It helps to separate them, because they carry very different weight.

• Sync. Your position, highlights and library, so they appear on your tablet. Genuinely useful, and it necessarily means a server knows which books you own and how far through you are.
• Telemetry. Crash reports, feature counters, session lengths. Usually mundane, occasionally detailed enough to reconstruct a reading session.
• Advertising and attribution SDKs. Third-party code whose purpose is to build a profile and match it to one held elsewhere. This is the category that is actually about you rather than about the app.
• Word lookups. Every definition or translation you request, sent as a query. The smallest-looking of the four, and the most revealing.

Why lookups give away the most

A list of books tells someone what you own. A list of the words you had to look up tells them which language you are learning, roughly how good you are at it, what you read at two in the morning, and which subjects you are quietly working through.

It arrives timestamped and in order, which makes it a diary. And because each lookup is one small request, it rarely feels like disclosure while you are doing it.

A book list is a library card. A lookup history is a transcript of what you did not understand.

None of this requires anyone to be acting in bad faith. Request logs are simply how servers work; a cloud lookup is a request; the record exists whether or not anybody ever reads it.

Checking an app yourself

You do not need tooling for this. Four checks, a minute each.

• The aeroplane-mode test. Turn the network off and tap a word. If the explanation still arrives, the work is happening on the device. If it fails, it was never local.
• The store privacy label. Both stores require a declaration. Look for "Data Used to Track You" and for identifiers — those imply an advertising graph rather than a reading app.
• Is an account required? To read a file already on your phone, an account is a choice, not a technical necessity.
• Read what the policy names. "We respect your privacy" is not a claim. "The text of your books is processed on your device and is not sent to our servers" is.

What a good policy actually says

Specific nouns, in short sentences. Which data, to whom, for what, for how long. Vague policies are usually vague on purpose: a promise that names nothing cannot be checked, and cannot be breached in any way you could demonstrate.

The strongest version is not a promise at all. An app that never receives your reading data cannot leak it, be compelled to hand it over, or change its mind in a future update. That is a property of the architecture rather than of the company's intentions, which is why it survives the company being acquired.

The honest trade-offs

Local processing is not free. The model has to live on your phone, which costs storage; it runs on your battery; and it will not be the largest model in the world. Sync across devices genuinely requires a server, so an app with no accounts cannot offer it.

Those are real costs, and worth stating plainly rather than pretending the choice is one-sided. What you get for them is that the list of words you did not know stays on the device where you did not know them.