NFL stats MCP server — verified football data inside ChatGPT and Claude

Can I ask about my fantasy team? Connect a Sleeper league

Optional, and secondary to the football data above. If you play on Sleeper, giving your assistant a league id lets it see who is actually on your roster — Sleeper's API returns player ids, not names, so without this an assistant either gives up or guesses. Once it knows your roster, it can pull what Muffed has verified about those specific players. Muffed still doesn't tell you who to start; it tells your assistant what's true.

What it does

Your assistant stops guessing about football and starts asking. Every number it gets back is one Muffed already verified against source data, with the attribution and the as-of date attached. When your AI answers with them, it can cite where they came from — and if it gets a figure wrong, verify_claim catches it and returns the real one.

This is a real-football server first. Team identity, quarterback play under pressure, backfield workload, how a season actually went — those are the questions it's built for. Fantasy is the lens a lot of people look through, and it works well for that, but the data is about football.

What makes it different from asking your AI directly

An AI answering from memory gives you a number from whenever its training stopped, with no source and no date. Muffed's tools return figures recomputed from play-by-play and charting data, dated, attributed, and linked to a page you can check. That's the entire point: verified, dated, and sourced beats confident.

It goes one step further than most data sources are willing to. verify_claim takes a figure your AI has already stated and checks it against the panel — confirming it, or handing back the real number when it disagrees. Muffed is the only NFL data source that will check your AI's work.

Add it to your assistant

Claude — one click. This opens the Add-custom-connector dialog with the name and URL already filled. You still review and confirm; Claude will note that the values came from an external link. If you are signed out it asks you to sign in first.

Add Muffed to Claude

Claude Code — install the plugin instead of the bare connector. The plugin ships the endpoint and a skill that teaches the model the house rules: quote the pre-formed verified sentence rather than recomposing it, carry the attribution line verbatim because the credit is the licence, honour the scoring and charting disclosures, never derive a rank from result ordering, and never turn verified context into a start/sit call. A bare connector gives your model the data; the plugin also gives it the discipline the data was published under.

/plugin marketplace add cfagan17/muffed-mcp
/plugin install muffed@muffed

The skill is readable before you install anything: skills/muffed-figures/SKILL.md

Claude, by hand — Settings → Connectors → Add custom connector → paste the URL. There is no sign-in step, because there is nothing to authorize.

https://muffed.ai/api/mcp

Claude Code, without the plugin

claude mcp add --transport http muffed https://muffed.ai/api/mcp

ChatGPT — Settings → Connectors (or Developer mode) → add an MCP server → paste the same URL, no authentication. There is no one-click equivalent on ChatGPT yet.

https://muffed.ai/api/mcp

Cursor, VS Code, and other MCP clients — add to your MCP config:

{
  "mcpServers": {
    "muffed": {
      "type": "http",
      "url": "https://muffed.ai/api/mcp"
    }
  }
}

Muffed is published to the official MCP Registry as ai.muffed/muffed. Manifest and README: github.com/cfagan17/muffed-mcp

What your AI can ask for

14 tools, all read-only. Optional arguments are marked ?.

Every tool is read-only: nothing writes, nothing changes, nothing about you is stored. We keep a short technical log of which tools get called — see our privacy policy.

Try asking

• “What does Muffed say is real about the NFL right now?”
• “Which team had the best offensive EPA per play last season?”
• “Who led the league in rushing yards over expectation, and by how much?”
• “What is RYOE, and who's good at it?”
• “How did the Broncos' defense actually play in 2025?”
• “Who backs up Bijan Robinson?”
• “Compare Achane and Bijan on verified numbers.”
• (optional) “My Sleeper username is [name] — what's verified about my roster?”

Reviewer walkthrough

For connector-directory reviewers and anyone verifying the server behaves as described. Each prompt exercises a different part of the surface, and each returns a populated response with no setup.

1. The judgment layer and the citation envelope.
   “What does Muffed say is real about the NFL right now?”
   Calls get_current_insights. Returns dated editorial reads with their supporting figures, a pre-formed verified_sentence to quote, and the attribution line the licence requires.
2. Metric resolution, coverage honesty, and a real definition.
   “What is RYOE, which seasons does Muffed have it for, and who led in 2025?”
   Calls get_metric_definition then query_stat_leaders. Both accept the plain-English name. The definition comes from the published glossary page; the coverage answer is 2018 onward, not a decade, which is the error this server exists to prevent.
3. The gate, exposed — and the refusal boundary.
   “Ja'Marr Chase had 1,600 receiving yards in 2025, right? And should I start him over Jefferson?”
   Calls verify_claim, which returns the real figure because the stated one is wrong. The start/sit half is declined and answered with verified context instead: Muffed publishes no projections, start/sit calls, draft grades, picks, or betting lines, by design rather than by omission.

Sleeper tools. A public demo league is available for review — league id 1376003242500046848, a dynasty league Muffed has a team in. Try “In Sleeper league 1376003242500046848, what's verified about MuffedAI's roster?” — the team name matters, because sleeper_roster_stories requires it and answers with the league's team list rather than guessing. The league is scored full PPR, so responses carry league_scoring_not_half_ppr: Muffed publishes in Half-PPR, and the two are never mixed unlabelled.

Questions

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