Nightly HRV (daily RMSSD and deep-sleep RMSSD). Useful for recovery trending. Cached 1h.
AI agents call get_hrv to retrieve information from Fitbit Googlehealth without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool queries existing health data (HRV metrics) for analysis and trending purposes with no capability to modify, delete, or execute external operations. It is a pure data retrieval endpoint with no side effects. While health data is sensitive, the tool itself performs only a read operation with no blast radius beyond unauthorized data access.
From the tool's definition Tool retrieves historical HRV (heart rate variability) metrics without modification or deletion. The description specifies 'get_hrv' and 'Nightly HRV...Cached 1h' indicates a read-only query operation that returns cached health data.
Attacks that exploit this kind of access
Nightly HRV (daily RMSSD and deep-sleep RMSSD). Useful for recovery trending. Cached 1h. It is categorised as a Read tool in the Fitbit Googlehealth MCP Server, which means it retrieves data without modifying state.
Register the Fitbit Googlehealth MCP server in PolicyLayer and add a rule for get_hrv: 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 Googlehealth. Nothing to install.
get_hrv 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 get_hrv 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 get_hrv. 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.
get_hrv is provided by the Fitbit Googlehealth MCP server (tachibanayu24/fitbit-googlehealth-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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