AI agents use heartbeat to create or update resources in A2AMCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your A2AMCP environment.
The heartbeat tool writes status/presence data to the shared Redis store, enabling the coordination system to track which agents are active. This is a reversible write operation (agents can go offline, heartbeats expire). It has minimal blast radius since it only updates transient state used for liveness detection, making it low severity despite being categorized as Write rather than Read.
From the tool's definition Tool name is 'heartbeat' and description states 'Send periodic heartbeat'. A heartbeat is a write operation that creates or modifies state in the Redis backend—specifically recording a timestamp or status message to indicate the agent is alive and active.
Documented attack patterns abuse exactly the kind of access heartbeat gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and A2AMCP, and nothing reaches the server without passing your rules. This is the rule we recommend for heartbeat:
{
"version": "1",
"default": "deny",
"tools": {
"heartbeat": {
"limits": [
{
"counter": "heartbeat_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}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.
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Send periodic heartbeat. It is categorised as a Write tool in the A2AMCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the A2A 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 A2AMCP. Nothing to install.
heartbeat is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
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.
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.
heartbeat is provided by the A2A MCP server (webdevtodayjason/a2amcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from A2AMCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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17 A2AMCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.