AI agents use append_sheet_values_tool to create or update resources in Apps Script MCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Apps Script MCP environment.
The name strongly implies writing/appending data to a Google Sheet, which is a reversible write operation. The description is empty, which lowers confidence. Based on sibling tools (append_doc_text_tool, create_doc_tool, etc.) this server pattern confirms write operations. Severity is medium as misuse could corrupt spreadsheet data but it is reversible.
From the tool's definition Tool name: 'append_sheet_values_tool' — 'append' and 'sheet_values' suggest adding data to a spreadsheet.
Documented attack patterns abuse exactly the kind of access append_sheet_values_tool gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Apps Script MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for append_sheet_values_tool:
{
"version": "1",
"default": "deny",
"tools": {
"append_sheet_values_tool": {
"limits": [
{
"counter": "append_sheet_values_tool_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}append_sheet_values_tool 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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append_sheet_values_tool. It is categorised as a Write tool in the Apps Script MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Apps Script MCP server in PolicyLayer and add a rule for append_sheet_values_tool: 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 Apps Script MCP. Nothing to install.
append_sheet_values_tool 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 append_sheet_values_tool 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 append_sheet_values_tool. 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.
append_sheet_values_tool is provided by the Apps Script MCP server (sam-ent/google-automation-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Apps Script MCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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60 Apps Script MCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.