NapkinBook: the canvas between data and decisions

Anyone can say “likely.”
You say 27%.

NapkinBook is a digital and computational whiteboard for people who make data driven decisions. Start from the evidance, and update with your beliefs over time. The board does recomputes as you work. Wire in real evidence, then share it so sharper people can try to break it.

Free to try. Sign in to save and sync your work.

Built by a superforecaster who’s worked with Microsoft AI.

0.19 Brier score vs a 0.28 field average

90% win rate

A canvas that computes

Circles hold values, squares do the math, wires carry the numbers between them. Nudge any input, and everything downstream, including your final number, recomputes the moment you let go.

Live collaboration, end-to-end encrypted

Send one link and someone sharper picks up your board with every number still live: same canvas, live cursors, live ink, no accounts to create. The link doubles as the key, so boards stay end-to-end encrypted and the server never sees your work.

Present it, phone in hand

Turn any board into an authored walkthrough. The camera flies step to step while your phone becomes the remote, carrying the current step, your speaker notes, and what-if sliders the whole room watches you move on the big screen.

Uncertainty is a first-class value

Base rates counted from real series, p10 / p50 / p90 fans, Monte Carlo bands. The board treats “how sure” as part of the answer, not a footnote.

The whole thesis on one board.

The base rate, the drivers, your live number, the crowd’s, and the data behind it all sit on one canvas, so you see the whole argument at a glance, not scattered across tabs. Pick a piece and its inspector appears. Let go and the board is clean again.

The NapkinBook app: the Forecast starter board with two reference-class base rates and tailwind/headwind pushes wired into a combine reading 39%, its inspector open showing the operation grid and the WHAT MOVES IT receipt, with the toolbar, board menu, and minimap around the canvas. — Circles hold values, squares compute, wires carry your number and the crowd’s into a live gap, with the data it rests on right beside it.

Made to be argued over, not screenshotted.

A thesis is worth more after someone’s tried to break it. Send the link, and whoever’s sharper than you can pull up the same board with every number still live, instead of a stale screenshot in a group chat. When you’re walking a room through your reasoning, hit Present and your phone becomes the remote, carrying the current step, your notes, and what-if sliders the whole room watches you move.

The reasoning stays on the board, so when it resolves, you can see why you were right, or how you fooled yourself.

The stage screen, a chrome-free view that follows the show full-screen.

Paired over the link, nothing touches a server

One board instead of five tabs.

Each of these tools is great at its one job. NapkinBook is where they meet: the data, the math, and your read in one place, where the crowd’s number and yours sit side by side.

Capability	NapkinBook	Excalidraw	Sheets	Tableau
Infinite freeform canvas	Yes	Yes	No	No
Live math on the canvas	Yes	No	Yes	Partial
Probability & uncertainty bands	Yes	No	Partial	No
Query your own data in SQL	Yes	No	Partial	Yes
Forward-looking, not just history	Yes	No	Partial	No
Reasoning saved beside the number	Yes	Partial	No	No
Present + phone remote	Yes	No	No	Partial

Built-in With effort Not really

Pricing that fits on a napkin.

Every feature: canvas, math, probability, SQL
Live collaboration, end-to-end encrypted
Present mode with the phone remote
Export any walkthrough as a standalone report
No account, no metering, no paywall to hit

Before you ask.

Put a number on your next call.

Start from a blank board and land on a number you can defend in minutes. Yours against the crowd’s, the gap live. Nothing to sign up for.

Anyone can say “likely.” You say 27%.