What is excalidraw-mcp CLAUDE.md?

A project instruction document for Excalidraw MCP, a server that lets an agent manipulate a live Excalidraw drawing canvas.

It is for developing and maintaining the Python server, TypeScript canvas service, React client, and their shared data formats.

It gives contributors the project context, constraints, setup commands, and development workflows needed to work safely.

How lesleslie/excalidraw-mcp configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to lesleslie/excalidraw-mcp. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/lesleslie/excalidraw-mcp/main/CLAUDE.md

Clone the repo

git clone --depth 1 https://github.com/lesleslie/excalidraw-mcp

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/instructions/lesleslie/excalidraw-mcp/claude-md/github.svg)](https://agentmods.dev/instructions/lesleslie/excalidraw-mcp/claude-md)

Your own site

<a href="https://agentmods.dev/instructions/lesleslie/excalidraw-mcp/claude-md"><img src="https://agentmods.dev/badge/instructions/lesleslie/excalidraw-mcp/claude-md/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/instructions/lesleslie/excalidraw-mcp/claude-md"><img src="https://agentmods.dev/badge/instructions/lesleslie/excalidraw-mcp/claude-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 1,263 This file is loaded in full into every session.

When invoked 1,263 The same file — it is already loaded in full.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.01263	$0.01263
Opus 5.5	$0.00505	$0.00505
Sonnet 5.5	$0.00253	$0.00253
Haiku 4.5	$0.00126	$0.00126

Measured 1mo ago against content hash 16e23ac5dee9, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

excalidraw-mcp CLAUDE.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

CLAUDE.md · 137 lines

How it starts

The opening of the file, as written. The whole thing — 137 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

For a shorter, tool-neutral bootstrap document, start with AGENTS.md.

Project Overview

excalidraw-mcp is a dual-language MCP server for manipulating a live Excalidraw canvas.

Core parts:

excalidraw_mcp/: Python FastMCP server and canvas-process supervision
src/: TypeScript canvas server, HTTP API, and WebSocket coordination
frontend/src/: React Excalidraw client

The Python server owns the MCP protocol surface and supervises the TypeScript canvas service.

Key Constraints

The Python and TypeScript halves must stay in sync on payload shape and element semantics.
The canvas server is process-managed by the MCP server unless the task explicitly targets standalone canvas work.
Element storage is in-memory; do not assume persistence unless you are adding it intentionally.
Environment-driven security settings must remain configuration, not code constants.

Development Commands

Setup

uv sync
npm install
npm run build

Main Workflows

uv run python excalidraw_mcp/server.py
npm run dev
npm run canvas
npm run production
npm run type-check
uv run pytest

Useful Validation

npm run build:frontend
npm run build:server
npm run test:coverage
uv run ruff check --fix

Quality Workflow

Use Crackerjack-aligned Python quality checks for the repo's CI path, and pair them with the TypeScript build, type-check, and test flow whenever a change crosses stacks.

Architecture Notes

The runtime path is:

MCP tool call in Python
HTTP call to the TypeScript canvas API
WebSocket broadcast to connected clients
canvas update in the React frontend

Keep responsibilities split this way:

Python: MCP interface, validation, process lifecycle, recovery behavior
TypeScript server: element state, HTTP API, WebSocket fanout
React: rendering and client synchronization

If a change crosses layers, update the shared types and confirm the request and response contracts still match.

Read the full file on GitHub · 137 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

1mo ago Changed · +4 lines · +71 tokens per session 16e23ac5dee9
2mo ago First seen · 133 lines · 1,192 tokens per session scan A 6e35d16c61f3

Subscribe to this mod's changes

excalidraw-mcp CLAUDE.md is an instructions file published in the GitHub repository lesleslie/excalidraw-mcp (15 stars, last pushed 1mo ago), licensed BSD-3-Clause. It adds 1,263 tokens to every session, about $0.0051 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

excalidraw-mcp CLAUDE.md next to 6 instructions from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
excalidraw-mcp CLAUDE.mdlesleslie/excalidraw-mcp	Instructions file	15	1mo ago	BSD-3-Clause	A	1,263	Claude Code
vscode buildNext.instructions.mdmicrosoft/vscode	Instructions file	195k	yesterday	MIT	A	9,719	GitHub Copilot
next.js AGENTS.mdvercel/next.js	Instructions file	143k	yesterday	MIT	A	7,461	Codex, OpenCode
langchain AGENTS.mdlangchain-ai/langchain	Instructions file	149k	yesterday	MIT	A	4,680	Codex, OpenCode
vscode oss-third-party-notices.instructions.mdmicrosoft/vscode	Instructions file	195k	yesterday	MIT	A	5,516	GitHub Copilot
vscode copilot-instructions.mdmicrosoft/vscode	Instructions file	195k	yesterday	MIT	A	3,093	GitHub Copilot
deepseek-harness AGENTS.mddeepseek-ai/deepseek-harness	Instructions file	274k	2d ago	MIT	A	4,313	Codex, OpenCode

excalidraw-mcp: Instructions file for Claude Code