AI agents call getHeartRate to retrieve information from FitBit MCP without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves heart rate data from a user's Fitbit device without modifying, executing code, or causing irreversible changes. It is a simple data query operation with minimal security risk—the primary concern would be unauthorized access to personal health data, but the tool itself performs no destructive or executable actions.
From the tool's definition Tool name 'getHeartRate' indicates a retrieval operation. The pattern matches sibling tools (getActiveZoneMinutes, getActivities, getBadges, etc.) which are all read-only data retrieval functions from the Fitbit API.
Documented attack patterns abuse exactly the kind of access getHeartRate gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and FitBit MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for getHeartRate:
{
"version": "1",
"default": "deny",
"tools": {
"getHeartRate": {}
}
}getHeartRate is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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getHeartRate. It is categorised as a Read tool in the FitBit MCP MCP Server, which means it retrieves data without modifying state.
Register the FitBit MCP server in PolicyLayer and add a rule for getHeartRate: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches FitBit MCP. Nothing to install.
getHeartRate is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the getHeartRate rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for getHeartRate. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
getHeartRate is provided by the FitBit MCP server (nitayrabi/fitbit-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from FitBit MCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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16 FitBit MCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.