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CLAUDE.md - Steam MCP Server

What is this?

An MCP (Model Context Protocol) server that exposes Steam Web API endpoints as structured tools for AI-powered IDEs. It is the companion server for the Steam Developer Tools Cursor plugin, which provides 30 skills and 9 rules for Steam/Steamworks development. The server provides 25 tools: 18 read-only and 7 write/guidance tools.

The plugin's skills reference these MCP tools to fetch live data from Steam - player stats, store info, workshop items, leaderboards, and more.

Architecture

src/
  index.ts              Entry point - creates McpServer, registers tools, starts stdio transport
  tools/
    getAppDetails.ts     Each file exports a register(server) function
    searchApps.ts        that adds one tool with its name, description,
    getPlayerCount.ts    zod input schema, and async handler
    ...
  utils/
    steam-api.ts         Shared fetch wrapper, URL builders, API key helper, error formatting
    errors.ts            Custom error classes (rate limit, missing key, unavailable)

Key patterns:

  • Each tool is a self-contained module that exports register(server: McpServer).
  • steam-api.ts provides steamFetch() which handles timeouts (15s via AbortController with TimeoutError), HTTP error detection (429 rate limits with up to 2 retries and exponential backoff, 5xx unavailable), and JSON parsing.
  • errorResponse() formats errors as MCP-compatible { isError: true } responses.
  • Tools that need an API key call requireApiKey() which reads STEAM_API_KEY from env and throws MissingApiKeyError with setup instructions if missing.
  • No-auth tools (getAppDetails, searchApps, getPlayerCount, getAchievementStats, getWorkshopItem, getReviews, getPriceOverview, getAppReviewSummary, getRegionalPricing, getNewsForApp) work without any configuration.

How to build and run

npm install
npm run build     # tsc - outputs to dist/
npm start         # node dist/index.js (stdio transport)
npm run dev       # tsx watch for development

How to test

Automated tests (vitest):

npm test            # single run
npm run test:watch  # watch mode

Tests cover error classes, steamFetch behavior (mocked fetch), retry logic, and Zod input validation for tools.

Manual testing via MCP inspector or by configuring as an MCP server in Cursor:

{
  "mcpServers": {
    "steam": {
      "command": "node",
      "args": ["dist/index.js"],
      "env": {
        "STEAM_API_KEY": "your_key_here"
      }
    }
  }
}

No-auth tools can be tested without setting STEAM_API_KEY.

Environment variables

Variable Required Description
STEAM_API_KEY For some tools Steam Web API key from https://steamcommunity.com/dev/apikey

Relationship to the companion plugin

This repo (Steam-MCP) provides the live API layer. The companion repo (Steam-Cursor-Plugin) provides the Cursor IDE integration (skills, rules, and workflows). Together they give developers a complete Steam/Steamworks development toolkit inside Cursor.