How Sketchbook started
A design brief written late on 5 October, then a notebook, a web app and an Android app built over the following day.
Sketchbook is a notebook, diary, sketchpad and scratch space in one. It is the long-lived home for the things that used to disappear: notes from a build, a link worth keeping, a photo of a wiring loom, a quick drawing made with a pen on a tablet. It is also the one place where its owner and any Claude Code session work on the same pages, from a browser, from a tablet with a pen, or from a phone.
It was built entirely with Claude Code, using the habits this guide describes: a written design, a plan broken into pieces, one agent per piece, and a review of every piece before it was merged.
The brief
The design was written and approved on 5 October 2026. The decisions in it were the owner’s, not defaults, and they still shape everything:
- Pages are plain markdown files. That keeps them simple for Claude to read and edit. A database sits alongside for search, and version control keeps the history of every file.
- Organise, archive and delete from a sidebar. Nothing is thrown away by accident: archived pages keep their original place, and deleted pages wait in the Trash for thirty days.
- Save what matters. Files shared through the short-lived file-share page get a “Save to Sketchbook” button. Only what is saved goes in.
- A private journal, locked behind its own PIN on top of the normal sign-in. It is editable, and it is never narrated, never shared and never sent anywhere else.
- Capture with provenance. Paste a link and the server fetches the asset and keeps a record of where it came from, who holds the copyright and under what licence.
- An Android app for the tablet and the phone: freehand drawing with the pen, notes and photos.
- Claude, four ways: any session can read and edit pages; a quick “ask Claude” for small questions; a session can ask for a sketch; and live sessions with no compromise.
- Mail inside the notebook, as the way off a desktop mail client. This was marked essential and moved into the first build.
- Interactive pages that can carry controls for things on the workbench.
One line in the brief set the bar for everything after it: the owner would maintain it himself and use it a lot, if the interface is right. So interface quality was written down as a requirement, not polish.
The first day of building
On 6 October the pieces were built in parallel and merged one by one.
The notebook itself. Pages with stable identifiers that survive moves and renames; move, archive, trash, restore and purge; a history of every change with the name of whoever made it; pictures and files stored once by their content; full-text search that ignores accents; a command-line tool and a set of tools Claude can call to work on pages; and an importer that brought the old logbook across with every original kept word for word. A nightly backup of the whole notebook was set up and a restore was tested the same day.
The web app. A sidebar of pages you can drag to reorganise, an editor that saves as you type and warns you if someone else changed the page, and a drawing canvas that responds to pen pressure, with pen, highlighter, eraser, lasso and undo. A command palette on Control and K searches titles, full text and commands. A History panel shows old versions and restores any of them. Later that day the editor gained a live preview, a formatting toolbar, tables you can edit in place, a slash menu, and paste from Word, Outlook, Google Docs and the web that comes in as clean markdown.
Live editing. Two people, or a person and Claude, can edit the same page at once and see each other’s cursors, and drawings update live. A test proved that two browser tabs and an edit made directly to the file on disk all end up with the same page.
Everything else from the brief. Capture that reads source and licence details from photos and web pages; a mail bridge that can read and draft, where sending only happens when a person presses Send; narration of a page with the section being read highlighted as it plays; page controls driven from an allow-list of devices, audited and rate-limited, with the device list shipped empty; read-only snapshots of a page behind an unguessable link that can be revoked at any time; a graph of how pages link to each other; page templates; checkboxes with a date that become phone reminders; a Claude section with sessions, chat and a terminal; and a 3D preview for STL and STEP files.
The Android app, built the same day: an offline copy of the notebook and a queue of changes that waits for a connection, pen drawing with pressure, tilt and palm rejection (the pen always wins over a resting hand), a share-sheet target that saves links and pictures to the Inbox, photo upload from the camera and gallery, the journal behind a PIN with optional fingerprint, a check for app updates, and a first version for the car: voice notes, asking Claude, and tasks. Its launcher icon is a pen nib, and the same nib became the mark in the sidebar and the favicon.