ClipSync

ClipSync keeps one clipboard in sync across your Android devices and your Windows PC, with text, images and files all supported.

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What it does

• Your devices connect to each other directly. Everyone dials everyone they can see and everyone listens, so a phone and a tablet on the same Wi-Fi talk to each other whether or not the PC is switched on.
• ClipSync also works as a simple file transfer tool: files are split into chunks and sent over several connections at once, an interrupted transfer resumes instead of starting over, and a file the other side already has is not sent again.
• On the same LAN, devices find each other by mDNS that requires no additional setup. With a DDNS name pointing at your PC over IPv6, a phone reaches it from mobile data too. When several devices on one network are offered the same file, only one of them downloads it over the expensive link and passes it to the rest.
• With root privileges, sync process is exempted from the system freezer and is restarted if the system kills it. Also usable without root in one direction. See below.
• Messages are encrypted with a pre-shared key that rotates automatically every couple of days, so nothing is readable in transit and a key that leaked stops being useful on its own.

Root, and what you get without root

Root and LSPosed buy exactly one thing: uploading while the app is not on screen.

Since Android 10, an app that is not in the foreground cannot read the clipboard, which is what upload needs, and there is no permission that grants it back. Download does not read the clipboard, so it is not restricted the same way. So on a device with no root:

Clipboard content direction	Without root	With root + LSPosed
Download	Works	Works
Upload	Won't work in the background	Works

A non-rooted phone therefore still works as a receiver, permanently and unattended, which covers the common case of "send this to my phone". To keep it connected, grant it what any long-running app needs on your ROM: exemption from battery optimisation, permission to autostart, and no background restriction. The app's own Allow card handles the first; the rest live in your ROM's settings and are worth locking in, because a killed process cannot receive anything either.

Install the APK normally and skip the LSPosed step. Nothing else changes.

What the module does, when you do have root

It hooks system_server and does three small things:

Hook	Why
ClipboardService.setPrimaryClipInternalLocked	Pushes every new clip straight to the sync service as soon as it changes, even while the app is in the background.
ClipboardService.showAccessNotificationLocked	Suppresses the "ClipSync pasted from your clipboard" toast for our own uploads.
The app freezer (ProcessRecord / Process.setProcessFrozen)	Keeps the sync process from being frozen while it holds the connection, and restarts it if the system kills it.

What you need

Item	Description
Android	15 or newer. Root and LSPosed (libxposed API 102) only for uploading
Windows	modern Windows with Python 3.9+ installed
For Internet use	IPv6 on both ends, a DDNS name pointing at the PC, and inbound TCP 47521 allowed in your router's IPv6 firewall
For LAN-only use	Nothing extra. Both on the same Wi-Fi, with client isolation off

You can start LAN-only and add the DDNS path later; the app chooses the fastest path automatically.

Download

The release contains two files:

File	What it is
app-release.apk	The Android app and Xposed module
windows.zip	The PC side: configurator.py, install.ps1, uninstall.ps1, and app\, which holds the service and everything it imports

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Setup

You do not need to make a key by hand. One device makes it and the rest take it over the network; the nine-digit code shown on the first device opens the channel, and the device holding the key asks you to confirm before it hands it over.

1. Windows

Unzip windows.zip somewhere permanent (it runs from where you put it), then:

.\install.ps1

It asks for administrator rights itself, so double-clicking is fine. It installs the Python packages it needs, opens the firewall ports, registers a task that starts ClipSync when you log in, and opens the settings window. It changes nothing else, and .\uninstall.ps1 reverts exactly those changes. your config, logs, received files and Python packages are left alone (the packages are listed so you can remove them yourself if nothing else wants them).

In the settings window, either:

• Generate random PSK key, if this is your first device, then Share this key… when you set up the next one; or
• Pair with a device…, if a phone is already set up: tap Pair new devices there, and type the nine digits it shows. It displays them in threes, as "123 456 789", and the spaces are only there to be read; type them or leave them out, either works.

If your devices will reach this PC at an address, turn on Direct connections and add it: a DDNS name, a static address, whatever applies. For a LAN-only setup there is nothing to add: Local network discovery is enough to be found. Press Apply.

2. Android (on each device)

1. Install app-release.apk.
2. (rooted devices) In LSPosed, enable ClipSync with scope System Framework, then reboot. On a device without root, everything except background upload works anyway.
3. Open the app. It walks you through setup the first time: choose I have another ClipSync device and enter the code the other one is showing, or This is my first device to make a key and hand it out. Set up ClipSync in Settings opens the same thing again later.
4. To reach a PC that is not on this network, turn on Direct connections and add its address. Local network discovery needs nothing configured. Then press Apply or Start.
5. If the app shows a battery card, tap Allow. It keeps Android from suspending the connection.

The status chip in the top-right corner tells you where you stand: Stopped, No network, Connecting…, Idle while the screen is off, or Connected (n). Tap it for a card per device, showing its name, id, type and address, and below those, every configured target that is not connected with the reason why. The Log tab shows everything as it happens.

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Tips

• Received files. They land in Download/ClipSync on Android and in the received folder next to clipsync.py on Windows. Files are put on the clipboard so you can paste them straight into a file manager. The file receive paths are all configurable.
• Size limits. 1 MB of text, 10 MB per file over the Internet, 100 MB per file on the LAN. All three are configurable.
• Big files. They are split into chunks and sent over 8 connections at once. If a transfer is cut off, the rest is resumed rather than restarted, and a file the other side already has is never sent twice.
• A screen that is off is disconnected, by design. It costs nothing while you are not using it, and it catches up the moment you wake it.
• Housekeeping. Received files older than 2 hours are deleted, and the folder is capped at 256 MB. Both are configurable; 0 disables either.

Settings

Everything below is in the app's Settings tab, and most of it also exists on the PC, in python configurator.py, which writes config.json. Fields are validated as you type on both, and Apply stays disabled until they are all valid.

Setting	Default	Notes
Port	47521	Must match the PC
PSK	none	64 hex characters, identical on every device. Generate random PSK key under the field makes one
Local network discovery	on	Find peers on this network by mDNS. Needs no configuration
Direct connections	off	Connect to addresses you list. A host name or a literal IPv4/IPv6 address, with dynamic DNS being one option, not a requirement
This device's addresses	empty	Names that point at this device, if any. ClipSync uses them to recognise itself, so it never dials itself and refuses one of them typed into the list above
mDNS browse timeout	4 s	How long to look for the PC on the LAN before giving up
Max text	1 MB	Larger clips are not sent
Max file (Internet)	10 MB
Max file (LAN)	100 MB
Parallel connections	8	1-16
Received files folder	Download/ClipSync	Anywhere under Download/ or Documents/
Keep for	2 h	0 keeps them forever
Keep at most	256 MB	0 for no limit

Settings are saved on the device and survive reboots and updates.

Troubleshooting

Symptom	What to check
Copies made while the app is in the background never arrive, but the PC to phone direction works	Expected on a device without root. On a rooted one it means the module is not active: download needs no hook, so a working PC to phone direction proves nothing. Enable ClipSync in LSPosed with scope System Framework and reboot.
Status stays Stopped or keeps reconnecting	Open the Log tab and the logs should name the reason. For example, direct path failed (name) means that address did not resolve or did not answer, typically because there is no IPv6 or no AAAA record on this network; local discovery is raced alongside it and takes over by itself.
mdns: no _clipsync._tcp service found	The PC is not advertising. Check clipsync.log on the PC: missing zeroconf, UDP 5353 blocked, or Wi-Fi client isolation.
Connected, but nothing arrives	PC firewall or router IPv6 inbound. clipsync.log should show the device connecting.
decrypt error in clipsync.log	The PSK differs between the PC and that device. This also happens on its own if a device has been off for more than about a week: the key has rotated past what it still has, and it needs to be paired again.
Works on one device, not the other	Both must appear as connected in clipsync.log. A device whose screen is off is disconnected on purpose.
The app logs process was suspended for ~N s	Android froze the sync process. Tap Allow on the battery card, and grant autostart / remove background restrictions in your ROM's settings. On a rooted device, also check that LSPosed still has the module enabled as the freezer exemption is part of the module.

If something still looks wrong, the Log tab has a Copy button; that log is what to attach to an issue. On the PC the same record is clipsync.log next to clipsync.py. It is capped at 128 KB: when it fills, it becomes clipsync.log.old and a fresh one starts, so there is always roughly the last two files' worth and never a log that grows without end.

Privacy and security

• The pre-shared key never leaves your devices. It is not derived from anything, not uploaded, and not recoverable. If you lose it, generate a new one and set it on every device.
• Every frame is encrypted and authenticated with ChaCha20-Poly1305 under a key derived per connection; a device that cannot prove it holds the PSK is disconnected before anything is read.
• The key rotates itself every 48 hours and the devices agree on the new one automatically; you do not need to do anything. A device that was switched off still connects when it comes back, since recent past keys keep working for about a week. Left off longer than that, it has to be paired again.
• Clipboard contents are held in memory. Files you receive are written to the folder you chose, and are deleted by the housekeeping settings above.
• The log records what happened, sizes, file names and peer names, but never clipboard text.
• The DDNS path is only used if you configure a name. Left empty and nothing ever leaves your LAN.

Building it yourself

Everything here is built from this repository by GitHub Actions; see .github/workflows/build-apk.yml for the exact steps, and android/ for the Gradle project. The PC side is a single Python file with no build step at all. Read windows/app/clipsync.py before you run it.

License

MIT