AI agents use update_vacation to create or update resources in Gmail MCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Gmail MCP environment.
This tool modifies vacation responder settings, which is a configuration change that can be undone (vacation auto-replies can be disabled, modified, or removed). It creates or modifies data reversibly without deleting data or executing arbitrary code. While it affects how emails are automatically handled, the change is not destructive or irreversible.
From the tool's definition Tool name 'update_vacation' and description 'Update vacation responder settings' indicate modification of account configuration settings.
Documented attack patterns abuse exactly the kind of access update_vacation gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Gmail MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for update_vacation:
{
"version": "1",
"default": "deny",
"tools": {
"update_vacation": {
"limits": [
{
"counter": "update_vacation_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}update_vacation 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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Update vacation responder settings. It is categorised as a Write tool in the Gmail MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Gmail MCP server in PolicyLayer and add a rule for update_vacation: 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 Gmail MCP. Nothing to install.
update_vacation 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 update_vacation 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 update_vacation. 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.
update_vacation is provided by the Gmail MCP server (shinzo-labs/gmail-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 65 Gmail MCP tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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65 Gmail MCP tools catalogued and risk-classified — across an index of 42,500+ MCP servers.