Short answers to the questions that bring people here, each with the mechanism and a place to check. Where the answer is about FrankenKeys specifically, it says so; the rest applies to any Android keyboard.
Does a keyboard app need internet permission?
No. A keyboard needs, at most, vibration for haptics and the microphone for voice typing through the system recogniser. Dictionaries can ship inside the app. Several keyboards hold no network permission at all, FrankenKeys among them, and the table of which ones do is read from their own listings. A keyboard that holds the permission usually has a reason, such as downloading language packs, and the vendor should state it.
Can a keyboard app read my passwords?
Technically, yes. Every keyboard receives every key you press and can read the field it is typing into, and password fields are marked with a flag the keyboard may honour or ignore. Android's own warning when you enable a keyboard says it "may be able to collect all the text you type, including personal data like passwords and credit card numbers". What a keyboard does with a password field is its own code, and where it could send it is its permission list. FrankenKeys learns nothing, suggests nothing and captures no clipboard in password fields, and holds no network permission. What a keyboard can see.
Can a keyboard app see what I type in other apps?
It sees what you type in whichever app it is currently the keyboard for, which is all of them, one at a time. It cannot see other apps' screens, other fields, or anything in an app that is not currently accepting text. It is not a screen reader.
What is the INTERNET permission on Android?
Android's reference: "Allows applications to open network sockets. Protection level: normal." Normal means it is granted silently at install and never appears in a runtime prompt or on the main Permissions screen. Without it, the operating system refuses the process a socket, whatever the app's code or any bundled library tries. How to check whether an app holds it.
How do I check what permissions a keyboard has?
Three ways. On the phone: Settings, Apps, the keyboard, Permissions, the three-dot menu, All permissions; network access appears under Other as "have full network access". On Google Play: the listing, About this app, App permissions, See more; this list is derived from the app's manifest and the developer cannot edit it. With adb: adb shell dumpsys package <package> and read the requested permissions. The full guide.
How do I stop my keyboard sending data?
If it holds the network permission, you can only turn off the features its vendor lets you turn off; Gboard's are walked through in Gboard's privacy settings, one by one. You cannot remove a permission from an app. If you want a keyboard that cannot send anything, pick one whose listing shows no network access, and confirm it with the check above.
What permissions does a keyboard app need?
Vibration, if it offers haptics. Microphone, if it offers voice typing. That is the list. FrankenKeys holds those two plus three that are not about you: a bind to Android's on-device AI service, Play Billing for the one-time unlock, and a private permission it uses to talk to itself. All five, with reasons.
Does FrankenKeys work without internet?
Yes, and it cannot work any other way: it holds no network permission. Typing, prediction, autocorrect and swipe run on the phone in all thirty languages, and the AI rewrites and voice typing run on the phone too. The rewrites are English only. The one asterisk is voice typing on Android 10 and 11, where the keyboard can only ask the system recogniser to stay offline; on Android 12 and later it requires the on-device recogniser. The voice page.
Is FrankenKeys open source?
No. Release builds ship unobfuscated, so anyone can decompile the installed app and read its code with the real class names, but the source is not published under a licence and you cannot rebuild it. HeliBoard, FlorisBoard and Urik are open source; FUTO is source-available. The comparison says so plainly, and why unobfuscated was the choice is its own post.
Does FrankenKeys have ads or a subscription?
No ads, no subscription, no account. It is free, with one one-time in-app purchase that unlocks the creation tools. The unlock page.
The word "spy" is absent from this page on purpose. The people who search it are usually looking to install one, and this is not the site for that.