heartbeat · Claude Sync MCP: Risk & Policy

WHAT IT DOES

What heartbeat does on Claude Sync

AI agents use heartbeat to create or update resources in Claude Sync — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Claude Sync environment.

WHY IT NEEDS A POLICY

Why heartbeat needs a policy

The heartbeat tool writes a liveness record (or timestamp) to indicate the agent is active. This is a low-impact write operation with minimal blast radius — misuse at worst results in false liveness signals, slightly disrupting coordination logic but causing no data loss or irreversible effects.

From the tool's definition 'Register that an agent is alive' — writes/updates liveness state for an agent in the shared system

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

heartbeat Rate-limited

heartbeat stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "heartbeat": {
      "limits": [
        {
          "counter": "heartbeat_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Claude Sync, so you can run agents against it safely.

FAQ

Questions about heartbeat

What does the heartbeat tool do? +

Register that an agent is alive. It is categorised as a Write tool in the Claude Sync MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on heartbeat? +

Register the Claude Sync MCP server in PolicyLayer and add a rule for heartbeat: 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 Claude Sync. Nothing to install.

What risk level is heartbeat? +

heartbeat is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit heartbeat? +

Yes. Add a rate_limit block to the heartbeat 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.

How do I block heartbeat completely? +

Set action: deny in the PolicyLayer policy for heartbeat. 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.

What MCP server provides heartbeat? +

heartbeat is provided by the Claude Sync MCP server (the-firmament/claude-sync). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.