Polar Fitness MCP Server

An MCP server that turns raw Polar device data into AI-ready fitness insights. Exercise samples, heart rate streams, sleep hypnograms, and recovery metrics are preprocessed into compact summaries — so an AI assistant can analyse days of health data without blowing its context window.

Quick Start

1. Register at admin.polaraccesslink.com — create a new API client, note your client_id and client_secret, and set the redirect URI to https://localhost:8080/callback.

2. Install

npm install
npm run build

3. Configure — add to your MCP client (Claude Code settings.json, Claude Desktop, etc.):

{
  "mcpServers": {
    "polar-accesslink": {
      "command": "node",
      "args": ["/path/to/polar-accesslink-mcp-server/dist/index.js"]
    }
  }
}

4. Authenticate — ask Claude to generate your authorization URL using your client ID, complete the browser flow, then exchange the code for an access token. Add the returned credentials to your config:

{
  "mcpServers": {
    "polar-accesslink": {
      "command": "node",
      "args": ["/path/to/polar-accesslink-mcp-server/dist/index.js"],
      "env": {
        "POLAR_ACCESS_TOKEN": "your_access_token",
        "POLAR_USER_ID": "your_user_id"
      }
    }
  }
}

5. Register your user — after restarting, ask Claude to call polar_register_user. This is required before accessing any data.

Related MCP server: Oura MCP Server

Features

• Exercise tracking — workouts with heart rate zones, training load, and preprocessed sample metrics (pace splits, power, altitude, cadence, HRV)

• Daily activity — steps, calories, active/inactive duration with hourly step buckets and activity zone breakdowns

• Sleep analysis — sleep score, stages (light/deep/REM), sleep architecture, and heart rate trends during sleep

• Continuous heart rate — 24/7 heart rate data with preprocessed half-hourly buckets (avg/min/max)

• Nightly recharge — ANS charge, HRV trends, and breathing rate analysis

• Cardio load — daily strain, tolerance, and load ratio metrics

• SleepWise alertness — hourly alertness predictions based on sleep quality

• Exercise downloads — export workouts in FIT, TCX, or GPX format

• Dual output — all tools support markdown (human-readable) or json (structured) response formats

Why Preprocessing Matters

The Polar AccessLink API returns raw sensor data — thousands of individual heart rate readings, comma-separated sample strings with tens of thousands of values, and per-minute hypnogram entries. Passing this directly to an AI assistant would consume most of the context window on a single tool call, leaving little room for conversation or multi-tool workflows.

This server preprocesses raw data into compact, meaningful summaries before it reaches the AI:

The result is that a full day of activity, sleep, and heart rate data fits comfortably in a few hundred tokens instead of tens of thousands — making multi-day queries and cross-domain analysis practical within a single conversation.

Tools

The server provides 13 tools across 5 domains.

OAuth

User Management

Exercises

Daily Activity

Health & Recovery

Data Retention

The Polar AccessLink API only provides access to recent data:

To preserve historical data, export regularly using polar_download_exercise or the json response format.

Troubleshooting

"Access Denied" errors

You need to register your user. Ask Claude to call polar_register_user after configuring your access token.

Invalid or expired authorization code

Authorization codes are single-use and expire quickly. Generate a new authorization URL and complete the flow again.

401 Unauthorized errors

Verify your client_id and client_secret are correct at admin.polaraccesslink.com.

No data returned

• Ensure your Polar device has synced with Polar Flow

• The API only returns recent data (see Data Retention)

If you prefer not to use Claude's OAuth helper tools:

1. Create an application at admin.polaraccesslink.com

2. Set your redirect URI (e.g., https://localhost:8080/callback)

3. Direct users to authorize:

   https://flow.polar.com/oauth2/authorization?response_type=code&client_id=YOUR_CLIENT_ID&redirect_uri=YOUR_REDIRECT_URI&scope=accesslink.read_all

4. Copy the code parameter from the redirect URL

5. Exchange the code for tokens:

   curl -X POST https://polarremote.com/v2/oauth2/token \
     -u "CLIENT_ID:CLIENT_SECRET" \
     -d "grant_type=authorization_code&code=AUTH_CODE&redirect_uri=YOUR_REDIRECT_URI"

6. Use access_token as POLAR_ACCESS_TOKEN and x_user_id as POLAR_USER_ID

7. Register your user:

   curl -X POST https://www.polaraccesslink.com/v3/users \
     -H "Authorization: Bearer YOUR_ACCESS_TOKEN" \
     -H "Content-Type: application/json" \
     -d '{"member-id": "YOUR_USER_ID"}'

License

MIT