Write on your iPad. It lands on the screen you’re already sharing.
Your Apple Pencil ink appears live inside Zoom, Teams or Meet — write equations by hand while you teach, on Mac or Windows. No second device in the call.
You can’t write x² + 6x + 9 with a mouse.
In a handwriting subject, the mouse is the wall. You can talk through an equation, but you can’t work it — not legibly, not at the speed of a lesson someone is paying for.
So people fix it the hard way: they join their own call a second time from a second iPad, just to share it as a whiteboard.
The workaround: join your own call twice
- Join the call again from the iPad
- Share that second screen
- Mute it before the pencil taps hit the mic
- Keep both batteries alive for the hour
CastPen: one device, already shared
Pick up the pencil. It’s already on the screen you’re sharing. One call. One login.
Draw there. It lands here.
CastPen mirrors your computer’s screen onto the iPad — the slide you’re sharing sits right under your pencil. Draw on it, and the ink lands on the computer the same instant. The iPad never joins the call; it’s a pen for the screen everyone is already watching.
Three steps, and then you forget it exists.
Share your screen as usual
Nothing changes about how you run the call. Zoom, Teams, Meet — whatever the student or client uses.
Pair once
Set it up the first time and forget it. After that the iPad is just there when you open it — no cable, no code, no second login.
Draw on the iPad
Your computer’s screen appears on the iPad, live. Draw over the slide, a PDF, or a blank board — full Apple Pencil pressure and tilt — and the ink lands on the computer instantly.
It works on Windows.
Every pencil-on-screen tool of this kind is built on Apple Sidecar — a feature that only exists between an iPad and a Mac. There is no Sidecar on a PC, so on Windows those tools simply don’t run. CastPen doesn’t use it. The same iPad works with the laptop your school, agency or client handed you.
CastPen
“Pair once, then it just connects.”
Sidecar-based tools
“Mac only, by construction.”
Made for whoever’s holding the pen.
Tutors
Work the problem in your own handwriting while your student watches it happen. Math, physics, chemistry — everything a mouse can’t write.
Teachers
Run the hybrid lesson from the laptop you’re already sharing. Underline the sentence, circle the mistake, keep the class moving.
Presenters & consultants
Circle the number that matters while everyone is looking at it. No laser pointer, no “can you see my cursor?”
Answers before you ask.
Is this sharing my iPad’s screen?
No — the opposite. CastPen mirrors your computer’s screen onto the iPad, so the slide you’re presenting sits under your pencil. You keep sharing the computer exactly as before; the iPad never joins the call.
Does my student or client need to install anything?
No. The ink lands on your computer’s screen, inside whatever you’re already sharing. The other side just sees your screen — nothing to install, nothing to join.
Which meeting apps does it work with?
All of them. CastPen draws on the screen itself, so it works wherever a screen share works — Zoom, Teams, Meet, Webex, a recorded lesson, or no call at all.
Can the other person draw back?
No — CastPen is one-way by design. You annotate; they watch. If you need a canvas both sides can write on, a collaborative whiteboard is the better tool for that job.
What do I need?
An iPad that works with Apple Pencil, and a Mac or Windows computer for the free companion app. No graphics tablet, no dongle.
Wired or wireless?
Wireless. Pair the iPad with your computer once; after that it reconnects on its own — no cable, no pairing code every session.
Will the ink lag?
Latency is the thing we obsess over — ink is built to land on your screen as you write it. The footage above runs at real speed; judge it there.
Mac and Windows,
from day one.
The desktop companion is free, and one iPad app covers both platforms. Start on the screen you already share.