AI agents use add_delegate 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 creates a new delegated access relationship, which is a reversible modification of account permissions rather than an irreversible deletion. However, it has significant security implications as it grants another user access to read and manage emails.
From the tool's definition Adds a delegate to the specified account - this modifies account access permissions and security settings by granting another user delegated access to the email account.
Documented attack patterns abuse exactly the kind of access add_delegate 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 add_delegate:
{
"version": "1",
"default": "deny",
"tools": {
"add_delegate": {
"limits": [
{
"counter": "add_delegate_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}add_delegate 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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Adds a delegate to the specified account. 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 add_delegate: 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.
add_delegate 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_delegate 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_delegate. 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_delegate 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.
Free to start. No card required.
65 Gmail MCP tools catalogued and risk-classified — across an index of 42,500+ MCP servers.