---

tags:

• whiteboard
• tldraw
• mcp
• tool
• plugin

---

Shared Whiteboard

Named, persistent draw.io-style whiteboards in the browser that you and Claude edit at the same time. Boards live on a small sync server; the browser renders them with tldraw; an MCP server lets Claude open a board by name and mutate it. Your edits and Claude's edits appear on the same canvas.

Install (Claude Code plugin)

The quickest way. Installs the MCP server and the sync backend + web UI in one step — no clone, no npm install (the plugin ships a self-contained bundle). Run these in Claude Code:

/plugin marketplace add camfung/shared-whiteboard
/plugin install shared-whiteboard@camfung-plugins

• Restart Claude Code when prompted so it loads the MCP server.
• On first use the plugin boots a local backend + web UI at http://127.0.0.1:5858 — open that in your browser to watch Claude draw live.
• Nothing else to configure: the plugin auto-spawns the backend for you. The manual Run and Claude / MCP sections below are only for running from source (development).

Update later: re-pull the marketplace, then reinstall:

/plugin marketplace update camfung-plugins
/plugin install shared-whiteboard@camfung-plugins

The workflow it's built for

1. Open the web UI, pick a board from the dropdown (or ＋ new). The dropdown name is what you tell Claude.
2. Tell Claude: "open the Auth Redesign board and add a node for the session store".
3. Claude calls open_board("Auth Redesign") then edits — you watch it happen live.
4. Either side can create boards; new boards show up in the other's list.

Skills

The plugin ships two skills that give Claude a scripted first step: boot the backend if it's down, then open the board in your browser — so you never end up with Claude drawing to a window you can't see.

• create — triggered when you ask Claude to draw, diagram, or add anything to the whiteboard. Opens the board, then guides Claude through create_node / create_uml / create_note / create_text / connect.
• edit — triggered when you ask Claude to move, restyle, connect, rename, re-layout, or delete existing shapes. Opens the board, then reads the current shapes before mutating them.

Each skill's open-board.sh is a thin wrapper over wb server open (pure Node — no curl or node_modules needed), so it works the same from a plugin install or a source clone.

Architecture

One authoritative document per board

• Each board is a TLSocketRoom (@tldraw/sync-core), keyed by a url-safe id.
• Two kinds of client mutate the same room: browsers (WebSocket, @tldraw/sync) and Claude (HTTP, via the MCP server).
• Every mutation runs through room.updateStore(...), which broadcasts to all connected browsers — so Claude's edits show up live, and get_board reflects edits you just made.
• Persistence: any change (browser or Claude) debounce-writes the board's snapshot to data/snapshots/<id>.json; it's reloaded on next access. Board names live in data/boards.json. Restarting the server keeps every board.

 browser (tldraw useSync) ──WS──┐
                                ├── server.js (TLSocketRoom per board) ── data/*.json
 Claude (mcp-server.js) ──HTTP──┘

Pieces

• server.js — sync backend. Browser WS at /connect/:boardId; semantic HTTP API; also serves the built web UI from web/dist when present (one port for everything).
• boards.js — named + persisted room registry (create/rename/delete/load/save).
• shapes.js — builders → valid tldraw v5.2.5 records (captured from a live editor).
• uml-schema.js — the custom uml shape's props (backend half; see caveat below).
• templates.js — reusable block store + stamp/clone (id remap, re-base to a point).
• mcp-server.js — stdio MCP. Holds a per-session "current board"; each tool = one HTTP call.
• web/ — Vite + React + tldraw client. Board picker, ＋UML, save/stamp templates.
  • web/src/uml.tsx — the UmlShapeUtil (browser half of the custom shape + double-click editing).

Custom UML shape — the one gotcha

A custom tldraw shape must be registered in three places, all agreeing on the same props (no migrations, so the synced schemas match):

1. web/src/uml.tsx — UmlShapeUtil.props (browser render + validation).
2. uml-schema.js → boards.js createTLSchema({ shapes: { uml: {props} } }) (server validation).
3. shapes.js buildUml (the record the MCP server writes). Change the props in one, change them in all three, or sync breaks.

Reuse model

No Figma-style linked masters (tldraw has none). A template is a captured bundle of records; stamping clones them with new ids at a target point. Copies are independent. Edit data/templates.json to inspect/prune.

Run (from source / development)

Skip this if you installed the plugin above — it bundles and boots everything. These steps are for hacking on the code or running a checkout by hand.

Dev (hot reload)

./run.sh            # backend :5858 + Vite dev UI :5173  → open http://127.0.0.1:5173

Always-on (one process serves UI + API on :5858)

cd web && npm run build          # build the UI once (rerun after web/ changes)
# then install the user service:
cp whiteboard.service ~/.config/systemd/user/whiteboard.service
systemctl --user daemon-reload
systemctl --user enable --now whiteboard.service
# UI + API now live at http://127.0.0.1:5858

The bundled whiteboard.service binds WB_HOST=0.0.0.0, so the board is reachable from other devices on the LAN (see On an iPad below).

On an iPad (installs as a full-screen app)

The UI is a PWA — added to the Home Screen it launches chromeless (no address bar, no tabs), locks out browser page-zoom so pinch drives the canvas, and kills the rubber-band bounce. It feels like a native app.

1. Serve on the LAN. The always-on service already binds 0.0.0.0. If you run it by hand instead, pass the bind explicitly:

   cd web && npm run build
   WB_HOST=0.0.0.0 node server.js      # UI + API on every interface, port 5858
   

   No auth — anyone on the LAN can read/edit. To scope it to your Tailscale net, use that interface's IP instead of 0.0.0.0.

2. Open it on the iPad. In Safari go to http://<this-machine-ip>:5858 (e.g. http://10.0.2.52:5858). hostname -I prints the machine's IPs.
3. Install. Share button → Add to Home Screen → Add. Launch it from the new "Whiteboard" icon — it opens full-screen.

Keep the iPad and host on the same network. The page and its WebSocket both talk to <the-host-you-opened>:5858, so LAN over plain http/ws just works.

Claude / MCP (from source)

Plugin users can skip this — /plugin install registers the MCP server via the bundled .mcp.json. This is the manual registration for a source checkout.

Registered at user scope (works in every project), pointing at the backend:

claude mcp add --scope user whiteboard --env WB_URL=http://127.0.0.1:5858 \
  -- node "/home/camer/ClaudeChats/Shared Whiteboard/mcp-server.js"

The MCP server just proxies HTTP, so the backend must be running (that's why always-on is recommended). Restart Claude Code to load the server after adding it.

Tools

Board management:

• list_boards — every board (name, id, shape count, updated).
• open_board {name} — open by name/id, make it active, return its contents.
• create_board {name} — create + open + make active.
• rename_board {name, id?} / delete_board {name}.

Reading the active board (call open_board or create_board first):

• get_board {since?, type?, color?, text?, ids?} — the whole board (shapes with id, type, x/y, w/h, color, text; uml shapes also give name/fields/methods) + arrow links + the board clock. Filters narrow it; since=<clock> returns only what changed. See Reading big boards efficiently below.
• list_shapes {type?, color?, text?} — compact index: one {id, type, label} line per shape (+ arrow links). A cheap map of a large board.
• get_shapes {ids?, type?, color?, text?} — full detail for specific shapes (by id, or by filter).
• get_neighbors {ids, hops?} — a shape plus everything arrow-linked to it, out to hops links (default 1), with the connecting arrows.
• check_overlap — layout-quality metrics (overlap ratio, worst offenders); decide/verify a re-layout.

Editing the active board:

• create_node {text,x,y,w?,h?,shape?,color?,fill?} → id.
• create_text {text,x,y,color?,size?} → id.
• create_note {text,x,y,color?} → id.
• create_uml {name,x,y,fields?,methods?,color?} → id. A UML class block (title + fields + methods compartments).
• update_uml {id,name?,fields?,methods?,color?,x?,y?,w?} — replace name/fields/methods.
• add_field {id,field} / add_method {id,method} — append one row (auto-grows).
• connect {fromId,toId,text?,color?,dashed?} → arrow that follows the shapes.
• update_node {id,text?,x?,y?,w?,h?,color?,fill?}.
• delete_shapes {ids} — also removes bound arrows.
• clear_board — wipe shapes/arrows (keeps the board).

Reusable templates (save a block once, stamp copies anywhere):

• list_templates — saved templates (name + shape count).
• save_template {name, ids} — capture the given shapes (+ arrows between them) from the active board as a template.
• stamp_template {name, x, y} — drop a fresh independent copy onto the active board.
• delete_template {name}.

Enums

• colors: black, grey, light-violet, violet, blue, light-blue, yellow, orange, green, light-green, light-red, red
• shapes (geo): rectangle, ellipse, diamond, triangle, hexagon, cloud, star, oval, pentagon, octagon, rhombus, trapezoid, x-box, check-box, heart
• fills: none, semi, solid, pattern
• Invalid enum → error (it would otherwise crash the browser's validator).

Reading big boards efficiently

On a large board, don't re-read the whole thing every time:

• Map first, then drill. list_shapes gives a cheap index; pull full detail for only the ids you need with get_shapes, or expand outward from a node with get_neighbors.
• Filter server-side. type / color / text (substring, case-insensitive) / ids on get_board, list_shapes, and get_shapes narrow the result before it's sent.
• Poll changes with the clock. Every read returns a clock. Pass it back as get_board {since: clock} to get only shapes changed since (plus deleted ids from tombstones) — the cheap way to see the human's latest edits instead of re-reading the board. The response carries the new clock; keep it for the next poll.

HTTP API (what the MCP server calls)

• GET /boards · POST /boards {name} · POST /boards/rename {id,name} · POST /boards/delete {id} · GET /boards/find?q=
• GET /board?board=<id> — semantic summary + clock. Optional since=<clock> (delta: changed shapes + deleted ids), and type / color / text / ids filters.
• GET /shapes?board=<id>&fields=index|full — index = compact {id,type,label}, full = full detail; same type/color/text/ids filters.
• GET /neighbors?board=<id>&ids=a,b&hops=1 — graph neighborhood of the given shape ids.
• GET /snapshot?board=<id> — raw tldraw snapshot.
• POST /node|/text|/note|/connect|/update|/delete|/clear?board=<id>
• POST /mutate?board=<id> — low-level {puts, deletes} escape hatch

Notes / limits

• Coordinates are tldraw page pixels; create_* place shapes at x,y (top-left).
• Conflict model is last-write-wins per record — fine for a human + Claude taking turns, not CRDT-grade for two people typing in the same text field at once.
• Backend host defaults to 127.0.0.1 (the server.js default); the bundled service overrides it to 0.0.0.0 for LAN/iPad use. Override with WB_HOST.