Inspiration
Writing with Apple Pencil feels physically lighter than leaning into a keyboard and mouse, but the Mac is still where many people write, edit, and work. Nib turns the iPad into a calm input surface for the Mac instead of shrinking the Mac into another remote-desktop screen.
What it does
Nib is a paired native iPad and Mac experience. In control mode, Apple Pencil moves and clicks the Mac pointer while fingers scroll. Pencil double-tap switches into a landscape writing surface. Nib recognizes settled handwriting, sends the exact revisioned text decision to the Mac, and removes matching ink only after the focused Mac field confirms insertion. Still-visible ink can be scratched out before it commits.
The iPad stays visually quiet: black canvas, white ink, a few clear modes, and immediate local feedback. The Mac companion handles pairing, live Accessibility state, event injection, recognition relays, and observable insertion receipts.
How we built it
Codex translated the product brief and rolling-ink safety rules into an Axis issue graph, then implemented the shared Swift protocol, both native apps, local Bonjour/NWConnection pairing, permission recovery, Pencil/finger separation, rolling ink, structured recognition, and an autonomous virtual-Pad/Mac-Input-Probe harness.
GPT-5.6 Luna is an optional Mac-relayed handwriting recognizer. Nib sends only a cropped ink-region image plus a client-owned region ID and revision, requests a strict structured decision, and rejects unknown or stale results before they can affect the UI. On-device Vision remains the private default; Cerebras Gemma 4 is retained as a comparison path.
Challenges
The most important bugs appeared only across the real two-device boundary. We fixed competing Mac app instances advertising different services, pairing approval that could hide behind the main window, reconnection noise surfacing as modal errors, and an ad-hoc debug signature that made macOS Accessibility treat each Xcode build as a different app.
The writing loop has an intentionally stronger success definition than “an event was posted”: iPad ink may disappear only after the focused Mac editor demonstrably accepted the text. The receipt and telemetry path records message, region, revision, focus, and outcome without logging raw handwriting or recognized text.
Accomplishments
Physical iPad + Apple Pencil testing confirms precise Mac pointer control, clicking, smooth finger scrolling, and reliable Pencil double-tap mode switching. The result feels like one coherent Apple Pencil-first input product rather than a collection of remote-control gestures.
What's next
Complete the handwriting fixture benchmark across on-device Vision, GPT-5.6 Luna, and Gemma 4; finish the focused-field compatibility battery; capture the signature two-device demo; and finalize the privacy/release audit.