What is foundryvtt-mcp CLAUDE.md?

A project guide for an MCP server that connects AI assistants to FoundryVTT, software for running tabletop role-playing games online. It documents the codebase, tools, commands, architecture, and data flow.

Use it when building, testing, formatting, linting, or tracing requests through the foundryvtt-mcp TypeScript project.

It gives the coding agent project-specific guidance instead of making assumptions about the technology or how the code is organised.

foundryvtt-mcp CLAUDE.md — Instructions file for coding agents by RN0000: A project guide for an MCP server that connects…

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods

npx agentmods add instructions/rn0000/foundryvtt-mcp/claude-md

Clone the repo

git clone --depth 1 https://github.com/RN0000/foundryvtt-mcp

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/rn0000/foundryvtt-mcp/claude-md.svg)](https://agentmods.dev/instructions/rn0000/foundryvtt-mcp/claude-md)

Your own site

<a href="https://agentmods.dev/instructions/rn0000/foundryvtt-mcp/claude-md"><img src="https://agentmods.dev/badge/instructions/rn0000/foundryvtt-mcp/claude-md.svg" alt="Measured on agentmods" height="20"></a>

Per session 936 This file is loaded in full into every session.

When invoked 936 The same file — it is already loaded in full.

Security scan A 0 findings. Scan, not verified.

Origin 100% copy Near-identical to another mod 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	$0.00936	$0.00936
Opus 5	$0.00468	$0.00468
Sonnet 5	$0.00187	$0.00187
Haiku 4.5	$0.00094	$0.00094

Measured 4d ago against content hash af24705b9e11, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-05, from the pricing page.

Security

Grade A, and why

foundryvtt-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 4d 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.

Origin

This is a copy

100% identical to foundryvtt-mcp CLAUDE.md — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

CLAUDE.md · 86 lines

How it starts

The opening of the file, as written. The whole thing — 86 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Project: foundryvtt-mcp

Model Context Protocol (MCP) server bridging AI assistants with FoundryVTT tabletop gaming software.

Tech Stack

Language: TypeScript (ES modules, .js imports for MCP SDK compatibility)
Runtime: Node.js (Bun as package manager)
Test: Vitest (unit + integration), Playwright (E2E)
Lint/Format: Biome (linting + formatting)
Validation: Zod schemas

Essential Commands

bun run build          # Compile TypeScript
bun run dev            # Development mode with hot reload
bun test               # Unit tests (Vitest)
bun run test:integration # Integration tests (needs :30001 container + .env.integration — prefer `just test-integration-docker`)
bun run test:e2e       # E2E tests (Playwright, headless)
bun run lint           # Lint code (Biome)
bun run lint:fix       # Auto-fix lint issues
bun run format         # Format code (Biome)
bun run test-connection # Test MCP→FoundryVTT connection

Architecture

Data Flow

AI assistant calls MCP tool → src/tools/router.ts
Router dispatches to handler → src/tools/handlers/
Handler queries cached worldData → src/foundry/client.ts
Response returned as MCP result

Key Modules

Module	Path	Purpose
Client	`src/foundry/client.ts`	Socket.IO connection, world state cache
Auth	`src/foundry/auth.ts`	4-step Socket.IO authentication
Config	`src/config/index.ts`	Zod-validated environment config
Tools	`src/tools/definitions.ts`	MCP tool schemas
Router	`src/tools/router.ts`	Request→handler dispatch
Types	`src/foundry/types.ts`	FoundryVTT entity interfaces

Authentication & transport selection

client.ts selects transport purely by whether FOUNDRY_API_KEY is set:

FOUNDRY_API_KEY unset → Socket.IO mode (default): authenticates with FOUNDRY_USERNAME/FOUNDRY_PASSWORD and loads full worldData.
FOUNDRY_API_KEY set → REST API mode: connects to the REST module's /api/status instead. This is a transport switch, not an additive layer — it does not run alongside the Socket.IO worldData path.
USE_REST_MODULE (seen in some .env/example files and the test-connection tips) is not read by src/config/index.ts — it is a no-op. Transport is decided solely by apiKey presence.

Read the full file on GitHub · 86 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.

4d ago First seen · 86 lines · 936 tokens per session scan A af24705b9e11

Subscribe to this mod's changes

foundryvtt-mcp CLAUDE.md is an instructions file published in the GitHub repository RN0000/foundryvtt-mcp (0 stars, last pushed 10d ago), licensed MIT. It adds 936 tokens to every session, about $0.0047 per session on Opus 5. A static security scan graded it A with 0 findings. It is 100% identical to foundryvtt-mcp CLAUDE.md, differing in 0 lines, and is treated as a copy.

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AGENTS.md instructions for openai/codex, covering rust/codex-rs, the codex-core crate, code review rules, crate api surface and model visible context.

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Working notes and architecture documentation for the new esbuild-based build system in build/next. Use when making changes to the new build pipeline (transpile/bundle commands, NLS plugin, source-map handling, resource copying, or self-hosting watch tasks).

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foundryvtt-mcp CLAUDE.md