If you’ve read the second Harry Potter book, you remember Tom Riddle’s diary: you write in it, the ink sinks into the page, and something on the other side writes back. Maxime Rivest built exactly that for reMarkable’s newest e-ink tablet. You write with a real pen on a real page-like screen, the page drinks your ink, and an answer writes itself back in handwriting. As an interfaces for LLMs, this is pretty novel. Instead of glowing screens, keyboard, and chat bubbles, you just use ink. It’s almost as magical as the fictional diary.
We had the older model of that tablet sitting in a drawer, mostly retired. And we have a ten-year-old who has read the second Harry Potter book several times. The nerd math did itself.
Written by hand: “Hello Tom, are you there?” The ink fades, and the diary answers: “I am always here, waiting in the margins of these pages. Who is it that writes to me so hesitantly?”
Saturday night — making it run at all
The diary was built for the newest tablet; ours is a generation older — different chip, different screen, and software that hadn’t been updated since 2023. Another tinkerer had already started adapting it, which gave us a head start. The rest of the evening was classic weekend-project archaeology: update the tablet’s software three years forward, sneak a community-made app launcher onto it, build the diary for a processor nobody builds for anymore, and then stare at the first launch — a flash of a window, then nothing — until the real culprit turned up (the old tablet and the new app were, quite literally, speaking different dialects of numbers).
None of this required genius. It required patience, a search engine, an AI pair-of-hands that never gets bored, and the willingness to plug a cable back in eleven times.
Sunday — making it feel enchanted
A magic diary that mostly works isn’t magic — a ghost of your handwriting surviving the vanishing act ruins the trick. So Sunday went to the details: ink written near the edge of the page was invisible to the diary (it thought the page was smaller than the screen); faded words left pale stains behind; there was no way to close the book. E-ink screens, it turns out, have two personalities — a fast one that smudges and a slow one that’s immaculate — and the trick is knowing when to use which: fast while the pen moves, one immaculate pass the moment the writing stops.
Our favorite fix wasn’t technical at all. How do you close an enchanted diary? You could tap the little ✕ we added. Or — our daughter’s suggestion, and obviously the correct one — you write goodbye on the page, and the book closes itself.
Night one — the interrogation
We told the diary who it would be talking to: a ten-year-old, a devoted fan, firmly a Ravenclaw. Then we handed it over.
She wrote one hundred and one pages the first night.
And she did not chat with Tom Riddle. She interrogated him. She tested him on things he couldn’t know (he’s a memory from 1943 — Harry hasn’t happened to him yet), confirmed him against things he could, and then went straight at the case like a tiny prosecutor:
her did you open the chamber of secrets yes or No
the diary Such directness — a Ravenclaw who demands absolute truths…
She got the confession. She caught his first cover story and didn’t buy it. And when he slid into his velvet speech about power and greatness, she answered with the entire moral philosophy a ten-year-old needs: “don’t kill!” — and, pages later, flat and unimpressed: “I do’nt fear you.”
She held her ground against a dark wizard for a hundred pages. The spelling wobbled. The spine never did.
The part where we edited a horcrux’s memories
Everything the diary remembers lives on the tablet itself, in plain files a parent can read — which we did, cover to cover. Most of it was wonderful. A few of Tom’s lines were too faithful to the book: relishing his darkest stories when she pressed for them, and that oily “let’s keep this our secret” register the character is written in.
So we did two things. We gave the diary house rules that outrank the character: no savoring cruelty, no secrets from parents, and if she ever brings a real-life problem to the page, Tom steers her — in his own theatrical voice — toward telling a grown-up. And then the delicious part: because the diary’s memory is just files, we went back and edited thirteen of his memories, rewriting his worst moments into regret. He still admits what he did — she earned that confession fair and square — but he no longer enjoys telling it. When she argues morality with him now, she wins.
Somewhere, a certain dark wizard is furious about what we did to his diary. We’re at peace with it.
What a crazy world
Step back and look at what a weekend is now: a tablet that was gathering dust holds a handwritten conversation with a fictional villain, played by an AI that reads a child’s actual pen strokes — and the whole thing was assembled at a kitchen table, between other errands, by describing problems out loud to a tireless assistant and deciding which of its fixes to keep.
But the machinery isn’t the part we’ll remember. The part we’ll remember is a kid, pen in hand, telling the monster no — and the monster, thoroughly outmatched, admitting she’s wiser than he was.