Create a webhook subscription for message events
AI agents use create_subscription to create or update resources in Mcp Ap2 — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Mcp Ap2 environment.
This tool creates a new subscription (reversible Write operation), not a read-only query or destructive deletion. While the server handles financial/payment contexts (AP2 — Google's Agent-to-Agent Payment Protocol), this specific tool does not move money or commit financial obligations; it configures event delivery infrastructure.
From the tool's definition Tool name 'create_subscription' and description 'Create a webhook subscription for message events' indicate creation of a new subscription resource that modifies system state by establishing a webhook endpoint for event delivery.
Documented attack patterns abuse exactly the kind of access create_subscription gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Mcp Ap2, and nothing reaches the server without passing your rules. This is the rule we recommend for create_subscription:
{
"version": "1",
"default": "deny",
"tools": {
"create_subscription": {
"limits": [
{
"counter": "create_subscription_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}create_subscription 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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Create a webhook subscription for message events. It is categorised as a Write tool in the Mcp Ap2 MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Mcp Ap2 MCP server in PolicyLayer and add a rule for create_subscription: 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 Mcp Ap2. Nothing to install.
create_subscription 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 create_subscription 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 create_subscription. 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.
create_subscription is provided by the Mcp Ap2 MCP server (@codespar/mcp-ap2). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Mcp Ap2, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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1300 Mcp Ap2 tools catalogued and risk-classified — across an index of 43,000+ MCP servers.