Developer MaximeRivest released an open-source project called riddle on July 4, transforming the reMarkable Paper Pro e-paper tablet into an AI-responsive handwritten diary, inspired by Tom Riddle's magic diary from Harry Potter. After users finish handwriting on the e-paper and lift the pen, the ink gradually fades away after about 2.8 seconds, and the AI responds with a handwritten font that animates the reply stroke by stroke back onto the page.
Ink fades after 2.8 seconds of pausing, Dancing Script handwritten font animates reply stroke by stroke
(Source: MaximeRivest)
According to MaximeRivest's description and demo, the interaction flow of riddle is: after the user handwrites text on the reMarkable Paper Pro and pauses, the ink gradually fades from the page after about 2.8 seconds; the device enters a "thinking" state and then animates the AI-generated reply back onto the page stroke by stroke using the Dancing Script handwritten font, creating the visual effect of "someone writing back to you in real time." MaximeRivest posted on X: "I love it when technology feels like magic."
Three-layer architecture of riddle: Rust core, C/C++ quill display engine, oracle AI backend
Based on MaximeRivest's technical explanation, the architecture of riddle is divided into three layers:
Rust core layer: handles the input of handwritten strokes and the animation effects of ink fading and compositing.
C/C++ quill layer: directly controls the e-paper display engine, bypassing the general UI middleware to reduce display latency.
oracle AI backend: referred to by the developer as the "soul of the diary," responsible for receiving text input and generating replies.
oracle backend supports multiple AI services: OpenAI, OpenRouter, Groq, or self-hosted local servers
According to MaximeRivest's technical documentation, the oracle backend by default supports an OpenAI-compatible API (/chat/completions format); as long as the service follows this format, the backend can be switched by modifying environment variables. Supported options include OpenAI official, OpenRouter, Groq, and user self-hosted local servers; a local trip mode is also available for lower latency.
riddle currently only supports the reMarkable Paper Pro hardware and is published on GitHub under the MIT license.
Frequently Asked Questions
How does the handwriting experience of riddle work?
According to MaximeRivest's demo, after the user handwrites text on the reMarkable Paper Pro and pauses for about 2.8 seconds, the ink gradually fades from the page; after the oracle AI backend processes the input, it animates the reply back onto the page stroke by stroke using the Dancing Script handwritten font, simulating the visual effect of "someone writing back."
Which AI backends does riddle support?
According to the technical documentation, riddle's oracle backend by default supports an OpenAI-compatible API (/chat/completions format), and can connect to OpenAI official, OpenRouter, Groq, or a self-hosted local server, switched via environment variables; it also supports a local trip mode to reduce latency.
Where can riddle be obtained, and what license does it use?
According to MaximeRivest's announcement, riddle is published on GitHub under the MIT license and is compatible with the reMarkable Paper Pro e-paper tablet.
