AI agents use add_subscriber to create or update resources in Listmonk MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Listmonk MCP Server environment.
This tool creates new subscriber records, which is reversible via delete or status change operations (evidenced by sibling 'change_subscriber_status'). It does not execute code, delete data irreversibly, or move money.
From the tool's definition Tool name 'add_subscriber' combined with server context (Listmonk newsletter/mailing list management) indicates creation of new subscriber records.
Documented attack patterns abuse exactly the kind of access add_subscriber gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Listmonk MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for add_subscriber:
{
"version": "1",
"default": "deny",
"tools": {
"add_subscriber": {
"limits": [
{
"counter": "add_subscriber_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}add_subscriber 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.
Free to start. No card required.
add_subscriber. It is categorised as a Write tool in the Listmonk MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Listmonk MCP Server MCP server in PolicyLayer and add a rule for add_subscriber: 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 Listmonk MCP Server. Nothing to install.
add_subscriber 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 add_subscriber 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 add_subscriber. 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.
add_subscriber is provided by the Listmonk MCP Server MCP server (rhnvrm/listmonk-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 29 Listmonk MCP Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
29 Listmonk MCP Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.