Fantasy Baseball for Claude

Let Claude look after your Yahoo Fantasy Baseball team. Ask it to check your roster, scout free agents, review your matchup, and — when you say so — add/drop players or set your lineup.

Everything runs on your own computer with your own Yahoo access. Nothing is uploaded to anyone, and you don't need to be technical to set it up.

💬 Once installed, just talk to Claude with "fantasy …" commands: fantasy start to set up, then fantasy show roster, fantasy my matchup, fantasy who should I add, and more.

New in v0.2: Claude can now pull advanced stats directly from Baseball Savant, FanGraphs, and the MLB Stats API — Statcast exit velocity, barrel rate, expected stats (xBA / xSLG / xwOBA), WAR, wRC+, sprint speed, and more — for any player or your entire roster at once.

Part 1 · Install the extension (about 2 minutes)

1. Download the extension. Go to the Releases page and download the file ending in .mcpb (it's named yahoo-fantasy-baseball.mcpb).

2. Open Claude Desktop. If you don't have it yet, get it from claude.ai/download.

3. Go to Settings → Extensions.

4. Drag the .mcpb file into the Extensions window (or click Install Extension and pick the file).

5. Click Install. Done — Claude now has the fantasy tools.

You can leave the Client ID / Client Secret boxes empty for now. We'll fill them in during the next part, and Claude will tell you exactly what to paste where.

Related MCP server: MLB SportRadar MCP Server

Part 2 · Connect your Yahoo team (about 3 minutes)

You only do this once. In a chat with Claude, type:

fantasy start

Claude will walk you through it. Here's what to expect:

a) Create your free Yahoo "app"

This is just how Yahoo hands you a personal key. Claude will point you to developer.yahoo.com/apps/create, where you:

• Application Name: anything (e.g. "My Fantasy Helper")

• Application Type: Installed Application

• Redirect URI(s): type oob

• API Permissions: check Fantasy Sports, then pick Read/Write

• Click Create App

Yahoo shows you two values: a Client ID and a Client Secret.

b) Give those two values to Claude

Either paste them into the chat (Claude will save them securely on your computer), or enter them in Settings → Extensions → Yahoo Fantasy Baseball. Then say fantasy start again.

c) Authorize and finish

Claude gives you a link. Open it, click Agree, and Yahoo shows a short verification code. Paste that code back to Claude. It will find your leagues, set your team as the default, and you're ready. 🎉

Stuck? Just type fantasy status and Claude will tell you what's left to do.

Part 3 · Talk to your team

After setup, use plain language. A few examples:

You can also just ask naturally, e.g. "Who on my bench should I start tonight?" or "Is there a better closer available than the one I have?" or "Which of my outfielders has the best hard-hit rate?"

What "analyze" pulls together

When you ask Claude to analyze a player it fetches live data from:

Results also include direct links to each player's page on Baseball Savant, MLB.com, Baseball Reference, and FanGraphs.

Leaderboard downloads are cached for one hour, so analyzing your full roster costs only one network round-trip per source.

⚠️ Roster changes always ask first. Adding/dropping players and setting your lineup change your real Yahoo team, so Claude shows you exactly what it's about to do and waits for your confirmation before making the change.

Want it to run on a schedule?

You can ask Claude Desktop to do this regularly — for example, "every morning, check my roster for injured or benched starters and suggest fixes." Use Claude's built-in scheduling/tasks; the extension just provides the fantasy tools.

Frequently asked

Is my data safe? Yes. Your Yahoo keys and login are stored only on your computer (in ~/.yahoo-fantasy-mcp/config.json, readable only by you) and in your OS keychain. Nothing is sent to any server but Yahoo's own API. Tokens are never logged.

Why do I need my own Yahoo app? Yahoo requires each person to use their own keys. It keeps everything under your control and means no shared secrets.

It says "rate limit" or "wait an hour." Yahoo limits very heavy use. Take a break and try again later.

Does this cost anything? No. The Yahoo app and this extension are free.

For developers

This is a local MCP server (Node.js + TypeScript, stdio transport) for the Yahoo Fantasy Sports v2 API.

npm install
npm run build          # compile TypeScript to dist/
node dist/cli.js auth  # optional terminal setup (instead of in-chat)
node dist/cli.js serve # run the MCP server over stdio
npm run pack           # build the .mcpb desktop-extension bundle

Use it with Claude Code (or any MCP client) from source

claude mcp add yahoo-fantasy-baseball \
  -e YF_CLIENT_ID=your_id -e YF_CLIENT_SECRET=your_secret \
  -- node /absolute/path/to/dist/cli.js serve

Or add it to a Claude Desktop claude_desktop_config.json manually:

{
  "mcpServers": {
    "yahoo-fantasy-baseball": {
      "command": "node",
      "args": ["/absolute/path/to/dist/cli.js", "serve"],
      "env": { "YF_CLIENT_ID": "your_id", "YF_CLIENT_SECRET": "your_secret" }
    }
  }
}

Tools

Onboarding: fantasy_status, fantasy_setup, fantasy_authorize, fantasy_select_team.

Read: list_leagues, get_league, get_teams, get_team_roster, get_team_stats_week, get_team_stats_season, get_matchups, get_team_matchups, get_player_stats, rank_players, get_transactions.

Analysis (no Yahoo auth needed — fetches from public APIs): analyze_player_stats, analyze_roster_stats.

Write (destructive — clients prompt to confirm): add_drop_player, set_lineup. Trade proposals/accepts are planned for a future version.

Credentials resolve from the saved config or the YF_CLIENT_ID / YF_CLIENT_SECRET environment variables (the latter is how the desktop extension passes the settings-form values). Releases are built and published automatically by GitHub Actions on a v* tag.

License

MIT