Write on the page with your pen. After a pause, the diary drinks your ink — your words fade into the paper — the page thinks for a moment, and an answer writes itself back in a flowing hand, stroke by stroke, then fades away.

No screen glow, no keyboard, no chat UI. Just ink appearing on paper.

This is the diary from the demo.

🪄 New to this? Start here

You need a reMarkable Paper Pro in developer mode with a launcher installed. If that sounds like a lot, it isn't — remagic walks you through turning on developer mode and sets up everything with one command. Come back here, drop riddle in, and start writing to Tom.

Already have xovi + AppLoad? Install from the remagic catalog, grab the prebuilt bundle, or build from source.

Install with remagic (easiest)

remagic install riddle     # checksum-verified download → AppLoad
remagic config riddle      # settings form in your browser (+ QR for phone)

Then in AppLoad: tap Reload, then The Diary. Write, and rest your pen. (Or install it from the Store app right on the tablet.)

Install the prebuilt bundle

1. Grab riddle-<version>.zip from the latest release and unzip it into a folder: unzip riddle-*.zip -d riddle
2. Copy the folder to your tablet: scp -O -r riddle root@10.11.99.1:/home/root/xovi/exthome/appload/
3. Add an API key: cp oracle.env.example oracle.env in that folder and put your RIDDLE_OPENAI_KEY in it (any OpenAI-compatible key). Or skip it to use pi.
4. In AppLoad: tap Reload, then The Diary. Write, and rest your pen.

⚠️ This modifies your device. The prebuilt bundle and the catalog build run in takeover mode: tapping The Diary stops the whole reMarkable UI and takes the screen. Leave with a 5-finger tap — xochitl restarts automatically. It runs as root and drives the e-ink engine directly. It has only been tested on a reMarkable Paper Pro (ferrari, aarch64, OS 3.26–3.27). It may not work on other models or OS versions, and you use it entirely at your own risk. Not affiliated with reMarkable AS. Keep SSH access working before you install anything — if anything ever wedges: ssh root@10.11.99.1 'systemctl start xochitl'.

How it works

 pen (raw evdev, full 4096-level pressure, hardware event rate)
   │ strokes
   ▼
 riddle ── idle 2.8s → commit page → PNG ──► oracle (resident LLM process,
   │                                          streams reply sentence-by-sentence)
   ▼ strokes (Dancing Script → skeletonized to single-pixel pen paths)
 display backend
   ├── qtfb        — windowed, inside xochitl (build-from-source flavour)
   └── quill       — full takeover: xochitl stopped, vendor e-ink engine
                     driven directly for instant ink (lowest latency there
                     is; what the prebuilt bundle runs)

• riddle/ — the app (Rust). Pen input, ink surface, handwriting synthesis (rasterize → Zhang-Suen thinning → stroke tracing → animated replay), the oracle process manager, and both display backends.
• quill/ — the takeover display host (C/C++). An epfb-re-style QImage-constructor interposition shim over the vendor libqsgepaper.so waveform engine, exposed as a small C ABI (quill_init / quill_buffer / quill_swap) that riddle links against with --features takeover. Also carries a small family of demos (scribble, a pen-to-glass latency test, plus map, image, and GIF renderers).

Gestures

Do this	And
Write, then rest the pen	The diary drinks your ink and Tom replies
Write "show me what I wrote about…"	The remembered page rises through the paper: the date, your own handwriting rewriting itself stroke by stroke, Tom's old reply — all in faded ink. Touch the pen anywhere and today's page returns
Write "what do you remember?"	Tom answers with a handwritten list of remembered moments
Flip the marker	Erase
Draw a large ?	Summon the built-in guide
Tap five fingers at once	Leave the diary (takeover mode)
Power button	The page turns to "The diary sleeps.", then the tablet suspends; press again to wake exactly where you were (takeover mode)

In the windowed (qtfb) flavour, xochitl keeps the touchscreen and the power button: close the diary from AppLoad instead.

The diary remembers

Every finished page is kept — your actual pen strokes, a transcription, and Tom's reply — so the diary can do three things:

• Follow the conversation. Recent pages ride along with each request, so Tom remembers what you wrote yesterday (both backends, same behavior).
• Conjure the past. Ask in ink — "show me the page about the garden", "find what I wrote on Tuesday" — and the diary rewrites that page in front of you, in your own hand, dated, in faded ink. No buttons, no lists, no chrome: the pen is the only interface.
• Answer from memory. "What do you remember?" gets a handwritten index.

Memories live only on the tablet, in plain files under /home/root/riddle-data/memories (delete the folder and the diary forgets; the last ~400 pages are kept). RIDDLE_MEMORY=off in oracle.env turns all of it off — no storage, and nothing extra sent with requests. Set RIDDLE_TZ_OFFSET (hours from UTC) so memory dates read right.

The oracle (the "spirit" in the diary)

The diary's replies come from a vision LLM that reads your handwriting from the committed page (sent as an inline PNG). There are two backends, chosen at startup — pick whichever you have:

Option A — any OpenAI-compatible API (easiest, zero setup)

Set an API key and riddle talks straight to an OpenAI-compatible /chat/completions endpoint. Works with OpenAI, OpenRouter, Groq, a local server — anything that speaks the format. No extra software on the tablet.

export RIDDLE_OPENAI_KEY="sk-..."                       # required
export RIDDLE_OPENAI_BASE="https://api.openai.com/v1"   # optional (default)
export RIDDLE_OPENAI_MODEL="gpt-4o-mini"                # optional; must see images
export RIDDLE_OPENAI_REASONING="low"                    # thinking models only
export RIDDLE_OPENAI_MAX_TOKENS="2000"                  # runaway guard

Any vision-capable model works. On the tablet these live in oracle.env next to the binary (see oracle.env.example, or just run remagic config riddle — it has one-tap presets for OpenAI, OpenRouter, and Gemini). Example with OpenRouter:

export RIDDLE_OPENAI_KEY="$OPENROUTER_API_KEY"
export RIDDLE_OPENAI_BASE="https://openrouter.ai/api/v1"
export RIDDLE_OPENAI_MODEL="openai/gpt-4o-mini"

Two gotchas with thinking models (Gemini 3.x, o-series): set RIDDLE_OPENAI_REASONING=low for faster first ink (some providers reject the field on non-thinking models — leave it unset there), and keep RIDDLE_OPENAI_MAX_TOKENS roomy — hidden reasoning tokens count against it, and a tight cap starves the visible reply.

Verify your setup before launching the diary:

riddle --oracle-test path/to/handwriting.png   # prints the streamed reply

Measured ~0.9–1.1 s to first ink on-device. The HTTPS is built into riddle (pure-Rust, no extra libraries).

Option B — pi (the power path)

If you already run pi, riddle will use a resident pi --mode rpc process kept warm (Node + your subscription auth loaded once), so each turn pays only model latency. Used automatically when RIDDLE_OPENAI_KEY is not set. Defaults (override in oracle.env): pi at /home/root/node/bin (RIDDLE_PI_BIN_DIR), provider openai-codex (RIDDLE_PI_PROVIDER), model gpt-5.4-mini (RIDDLE_PI_MODEL).

Both stream the reply sentence-by-sentence, so the quill starts writing seconds before the model finishes. The persona prompt lives in riddle/src/oracle.rs.

A note on Tom's memory: with the HTTP backend every page is a fresh conversation — Tom does not remember your previous page. With pi, the warm session remembers everything since the diary was opened (and pi persists that session in its own data dir on the tablet).

If the oracle can't answer — missing key, refused key, no Wi-Fi — Tom writes the reason on the page instead of a reply, and the full error goes to the journal (journalctl -u riddle-takeover).

Building

Cross-compiled from x86_64. Two flavours:

Windowed (AppLoad/qtfb) — build from source

The bundles above are the takeover flavour; the windowed flavour must be built. Requires xovi + AppLoad on the device.

cd riddle
cargo build --release --target aarch64-unknown-linux-gnu

Install the binary to /home/root/xovi/exthome/appload/riddle/ with an external.manifest.json that sets "qtfb": true and points "application" at the binary itself (the manifest in this repo is the takeover one — AppLoad only hands riddle a window, via QTFB_KEY, when qtfb is true).

Takeover (instant ink) — the one from the demo

Requires the reMarkable SDK toolchain (~/rm-sdk-3.26) because the linked vendor Qt libs need its glibc, and libqsgepaper.so pulled from your own device (it is proprietary and not distributed here):

cd quill && ./build.sh              # pulls libqsgepaper.so from the device over
                                    # ssh, builds libquill.so + the demos
cd ../riddle && ./build-takeover.sh
./scripts/make-bundle.sh            # stages the AppLoad bundle in dist/riddle/

The staged dist/riddle/ is self-contained (binary, libquill.so, launch scripts, manifest) — copy it to /home/root/xovi/exthome/appload/riddle/, or publish it to the catalog with remagic publish dist/riddle. Launching via AppLoad (appload-launch.sh) detaches into a transient systemd unit, stops xochitl, runs the diary, and always restores xochitl on exit — leave with a 5-finger tap or SIGTERM (systemctl stop riddle-takeover); the power button sleeps and wakes the diary without leaving it. The unit's stop hook restarts xochitl even if riddle dies uncleanly. If anything wedges: ssh root@10.11.99.1 'systemctl start xochitl'.

What leaves the device

• Each committed page is rasterized to a small grayscale PNG and sent to the oracle you configured — nothing else ever leaves the tablet, and there is no telemetry.
• The PNG (/tmp/riddle-page.png) is deleted as soon as the oracle has read it; set RIDDLE_KEEP_PAGE=1 to keep the last page around for debugging.
• riddle never writes replies to disk. The pi backend, however, keeps its own session history in its data dir — the HTTP backend keeps nothing.
• Tom stays in character by design: the persona prompt (see riddle/src/oracle.rs) tells the model it is the diary and nothing else.

Fonts

The reply hand is Dancing Script (SIL OFL 1.1 — see riddle/fonts/OFL.txt).

License

MIT for everything in this repository (see LICENSE). The vendor libraries it interposes (libqsgepaper.so, Qt) are not included and must come from your own device/SDK.