Set a formula on a cell (e.g.
AI agents use numbers_set_formula to create or update resources in Iwork — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Iwork environment.
The tool modifies spreadsheet data by setting formulas in cells, which is a write operation. Severity is high because a malicious actor could inject formulas that extract sensitive data, trigger unintended calculations, or modify downstream dependent cells across the spreadsheet. However, it is not Destructive (data can be undone/reverted) and not Execute (it doesn't run arbitrary code, only spreadsheet formulas).
From the tool's definition Tool name 'numbers_set_formula' and description 'Set a formula on a cell' indicate modification of spreadsheet cell contents. This is a write operation that creates or modifies data in a reversible manner.
Documented attack patterns abuse exactly the kind of access numbers_set_formula gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Iwork, and nothing reaches the server without passing your rules. This is the rule we recommend for numbers_set_formula:
{
"version": "1",
"default": "deny",
"tools": {
"numbers_set_formula": {
"limits": [
{
"counter": "numbers_set_formula_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}numbers_set_formula 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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Set a formula on a cell (e.g. It is categorised as a Write tool in the Iwork MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Iwork MCP server in PolicyLayer and add a rule for numbers_set_formula: 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 Iwork. Nothing to install.
numbers_set_formula 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 numbers_set_formula 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 numbers_set_formula. 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.
numbers_set_formula is provided by the Iwork MCP server (reichenbach/iwork_mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Iwork, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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114 Iwork tools catalogued and risk-classified — across an index of 43,000+ MCP servers.