Fantasy Baseball for Claude & Codex

Manage your fantasy baseball team by chatting with Claude or Codex: check your roster, scout free agents, review your matchup, and analyze players with Statcast and FanGraphs data. Everything runs locally with your own Yahoo login — nothing is hosted, and your credentials stay on your machine.

We support a broad range of operations (league, team, roster, matchup, and player stats) via Yahoo's Fantasy Sports API. Lineup adjustments and add/drop actions go through browser-based workflows (Claude in Chrome or the Codex browser plugin), as Yahoo's write-scope API is deprecated.

Contents

• Install
  • Claude Desktop
  • Codex desktop app
• Connect your Yahoo team
• Talk to your team
• What "analyze" looks up
• Help
• License

Install

Pick the app you use — you only need one. Then continue to Connect your Yahoo team.

Claude Desktop

1. Add the extension

1. Download fantasy-baseball-vX.X.X.mcpb from the Releases page.
2. In Claude Desktop, go to Settings → Extensions.
3. Drag the file into the Extensions window and click Install.

Leave the Client ID / Client Secret boxes empty for now — you'll fill them in during Connect your Yahoo team.

2. Add the Fantasy Baseball skill (guided start/sit and roster-review workflow)

1. Download fantasy-baseball-skill-vX.X.X.zip from the Releases page.
2. Go to Settings → Capabilities and turn on code execution.
3. Go to Customize → Skills, click + → Create skill → Upload a skill, and choose the ZIP.

Codex desktop app

Requires Node.js (nodejs.org/download — install the LTS build). The plugin bundles the Yahoo tools and the Fantasy Baseball skill in one step.

1. In the Codex app, go to Settings → Plugins → Add plugin marketplace.

2. Add from a GitHub repo:

   • Source: dingyiyi0226/fantasy-baseball-mcp
   • Git ref: master
   • Sparse paths: (leave blank)

3. Open the Fantasy Baseball marketplace and install the Fantasy Baseball plugin.

4. Sign in to Yahoo in Codex's in-app browser (one time, for lineup and add/drop moves).

   The Yahoo authorization below lets the plugin read your roster. Browser-driven lineup and add/drop moves also need Yahoo Fantasy to be logged in inside Codex's in-app browser. In a Codex chat, ask:

   Open https://baseball.fantasysports.yahoo.com in the in-app browser so I can sign in.

   When the in-app browser tab opens, sign in to Yahoo there. After that, adjust-lineup and add-drop-player workflows can use the same in-app browser session. If a workflow opens Yahoo and finds that the tab is not logged in, it will stop and report the login state as an error instead of trying another browser.

Connect your Yahoo team

You only do this once, and it's the same in both apps: type fantasy start in a chat and follow the prompts.

a) Create your free Yahoo app

Yahoo requires each person to use their own keys. 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 then gives you a Client ID and a Client Secret.

b) Enter those keys

Paste the Client ID and Client Secret into the chat when asked, then say fantasy start again. (In Claude Desktop you can instead enter them under Settings → Extensions → Fantasy Baseball.)

c) Authorize and finish

Open the authorization link and click Agree. If your browser warns about a self-signed certificate, click Advanced and continue to localhost. Once you see Authorization complete!, say fantasy authorize.

The assistant will find your leagues, set your default team, and finish setup.

Stuck? Type fantasy status to see what's still missing.

Talk to your team

| Say this... | To do this | | --- | --- | | 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 strong free-agent options | | fantasy hot free-agent batters | Rank available hitters by recent Yahoo stats | | fantasy MLB leaders | Rank all Yahoo baseball players by a stat or overall rank | | fantasy my stats this week | Show your team's weekly totals | | fantasy recent moves | List recent adds, drops, and trades | | who's pitching tomorrow | List probable starting pitchers for a date (add "and who's a free agent" for ownership) | | analyze Shohei Ohtani | Pull Statcast, xStats, FanGraphs WAR/wRC+, and recent splits | | analyze my roster | Run the same analysis for every player on your roster |

You can also ask naturally, like "Who on my bench should I start tonight?"

What "analyze" looks up

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

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

Help

• FAQ and troubleshooting — data safety, rate limits, and letting analyze reach the stats sites.
• Developer notes — building from source and the full tool list.

License

MIT