Lousa

A whiteboard where your AI agent draws its explanations.

Your agent drawing a rate limiter explanation, stroke by stroke

Ask your agent "explain this visually" and it sketches an animated, hand-drawn diagram on a live board — instead of another wall of text. Lousa is an MCP server + web viewer: the agent authors a declarative scene (boxes, arrows, cylinders, notes), and the board renders it stroke by stroke, as if someone were drawing it in front of you.

Lousa is Portuguese for the classic school blackboard.

Why it's different

The agent is the artist. No prompt box, no OCR — your coding agent already has the context and draws through typed MCP tools.
Live, incremental drawing. Follow-ups edit the scene; the open tab animates only what changed, like watching the diagram evolve.
Point at things. Click elements in the viewer to select them, then tell your agent "improve what I selected" — it reads your selection through get_selection and targets exactly that.
Boards expire by default (12h, sliding) — a whiteboard, not a document graveyard. ttlHours: 0 keeps a board forever.

Quick start

Requires Node.js 18.17+.

# Claude Code
claude mcp add lousa -- npx -y lousa mcp

# or run the server directly
npx lousa            # viewer at http://127.0.0.1:4666

Any MCP host works — for stdio configuration use command npx, args ["-y", "lousa", "mcp"]. The stdio endpoint auto-starts the local server, so the viewer is always available. Then ask your agent to "draw how our auth flow works" and open the URL it returns.

MCP tools

Tool	What it does
`create_board`	Creates a board from a scene, returns `{id, url}`
`update_board`	Replaces the scene; unchanged elements stay byte-identical so only changes animate
`get_board` / `list_boards`	Read boards
`get_selection`	What the user selected in the viewer (ids + full elements)
`delete_board`	Deletes a board

The scene is a JSON array of elements — box, ellipse, diamond, cylinder, arrow (connects ids), line, text, note — rendered with rough.js. The full schema ships inside the tool definitions; agents need no extra setup.

Self-hosting a shared server

Run lousa on any Node host and point machines at it:

LOUSA_TOKEN=<secret> HOST=0.0.0.0 npx lousa        # server
LOUSA_URL=https://your-host LOUSA_TOKEN=<secret> npx lousa mcp   # each client

LOUSA_TOKEN gates board listing/creation/deletion and /mcp; per-board URLs act as capability links. AWS Lambda + S3 deployment is supported out of the box (lambda.js handler + LOUSA_BUCKET for storage); any HTTPS front (API Gateway, etc.) works.

Env var	Default	Purpose
`PORT` / `HOST`	`4666` / `127.0.0.1`	server bind
`LOUSA_DATA_DIR`	`~/.lousa/boards`	filesystem board storage
`LOUSA_BUCKET`	—	use S3 storage instead of filesystem
`LOUSA_TOKEN`	—	require bearer token (header or `?t=`) on global routes and MCP
`LOUSA_URL`	—	`lousa mcp` proxies to this remote server
`LOUSA_DEFAULT_TTL_HOURS`	`12`	default board expiry

Development

npm install
npm test          # node --test
node cli.js       # local server