Fantasy Baseball for Claude

A Claude Desktop Extension — drag the .mcpb file into Claude and you're done. No npm, no terminal, no config files.

Let Claude look after your Yahoo Fantasy Baseball team: check your roster, scout free agents, review your matchup, and more. Everything runs on your own computer with your own Yahoo access.

Note: Adding/dropping players and setting lineups are not supported — Yahoo has deprecated the write-scope Fantasy Sports API (yfpy#79).

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Part 1 · Install

1. Download yahoo-fantasy-baseball-vX.X.X.mcpb from the Releases page.
2. Open Claude Desktop — get it at claude.ai/download if needed.
3. Go to Settings → Extensions.
4. Drag the .mcpb file into the Extensions window and click Install.

Leave the Client ID / Client Secret boxes empty for now — you'll fill them in during setup.

Part 2 · Connect your Yahoo team

You only do this once. In a chat with Claude, type fantasy start and follow the prompts.

a) Create your free Yahoo app

Go to developer.yahoo.com/apps/create and fill in:

• Application Name: anything (e.g. "My Fantasy Helper")
• Homepage URL: https://localhost:8488
• Redirect URI(s): https://localhost:8488/callback
• OAuth Client Type: Confidential Client
• API Permissions: Fantasy Sports → Read
• Click Create App

Yahoo gives you a Client ID and Client Secret.

b) Give those values to Claude

Paste them into the chat, or enter them in Settings → Extensions → Yahoo Fantasy Baseball, then say fantasy start again.

c) Authorize and finish

Click the link Claude gives you, then click Agree. If your browser warns about a self-signed certificate, click Advanced → Proceed to localhost. Once you see "Authorization complete!", say fantasy authorize. Claude will find your leagues, set your team as default, and you're ready. 🎉

Stuck? Type fantasy status and Claude will tell you what's left.

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Part 3 · Talk to your team

Say this…	…and Claude will
fantasy show roster	Show your current roster
fantasy my matchup	Summarize this week's matchup
fantasy standings	Show league standings
fantasy who should I add	Find the best free agents
fantasy my stats this week	Show your team's weekly totals
fantasy recent moves	List recent adds, drops, and trades
analyze Shohei Ohtani	Pull Statcast, xStats, FanGraphs WAR/wRC+, and recent splits
analyze my roster	Run the above for every player on your roster

You can also ask naturally: "Who on my bench should I start tonight?" or "Is there a better closer available?"

What "analyze" pulls

Source	Stats
MLB Stats API	Season totals + 14-day & 30-day splits
Baseball Savant	xBA, xSLG, xwOBA vs. actual; exit velocity, barrel %, hard-hit %
FanGraphs	WAR, wRC+/FIP/xFIP, K%, BB%, SwStr%, GB/FB%

Analysis automatically targets your league's scoring categories. Results include links to each player's page on Baseball Savant, MLB.com, Baseball Reference, and FanGraphs. Leaderboard data is cached for one hour.

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FAQ

Is my data safe? Your Yahoo keys are stored only on your computer (~/.yahoo-fantasy-mcp/config.json) and in your OS keychain. Nothing is sent anywhere but Yahoo's API.

Why do I need my own Yahoo app? Yahoo requires each person to use their own keys — no shared secrets.

Rate limit errors? Yahoo limits heavy use. Wait an hour and try again.

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

analyze commands fail with a connection error? Claude may need explicit permission to reach the stats APIs. Go to Settings → Capabilities (Team/Enterprise: Organization settings → Capabilities) and add these under Additional allowed domains:

Domain	Used for
statsapi.mlb.com	MLB Stats API
baseballsavant.mlb.com	Statcast / expected stats
www.fangraphs.com	FanGraphs WAR/wRC+

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For developers

Local MCP server (Node.js + TypeScript, stdio transport) for the Yahoo Fantasy Sports v2 API.

npm install
npm run build          # compile TypeScript → dist/
node dist/cli.js auth  # optional terminal auth
node dist/cli.js serve # run MCP server over stdio
npm run pack           # build .mcpb bundle

Use with Claude Code or any MCP client

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 to claude_desktop_config.json:

{
  "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_login, fantasy_authorize, fantasy_logout, 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_league_scoring_categories, get_transactions

Analysis (no Yahoo auth — public APIs): analyze_player_stats, analyze_roster_stats (accepts optional playerKeys array, max 10 per call)

Write (deprecated by Yahoo — require force: true): add_drop_player, set_lineup

Credentials resolve from the saved config or YF_CLIENT_ID / YF_CLIENT_SECRET env vars. Releases are published automatically by GitHub Actions on a v* tag.

License

MIT