heartbeat · Todos MCP: Risk & Policy

WHAT IT DOES

What heartbeat does on Todos

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

WHY IT NEEDS A POLICY

Why heartbeat needs a policy

This tool creates or modifies data (the last_seen_at timestamp) reversibly. It is a straightforward Write operation with minimal blast radius - updating a timestamp cannot cause harm to other data, delete information, execute code, or affect finances. The operation is idempotent and easily undone. Severity is low because the scope of impact is narrowly limited to one agent's status field.

From the tool's definition Tool description states 'Update your last_seen_at timestamp' - this is a direct modification operation that changes the last_seen_at field in the system state.

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 Todos, so you can run agents against it safely.

FAQ

Questions about heartbeat

What does the heartbeat tool do? +

Update your last_seen_at timestamp to signal you. It is categorised as a Write tool in the Todos 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 Todos 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 Todos. 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 Todos MCP server (@hasna/todos). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.