Assign a category to a transaction. Args: transaction_id: The ID of the transaction to categorize category_id: The category ID to assign
AI agents use categorize_transaction to create or update resources in Monarch — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Monarch environment.
While the tool operates on financial data within Monarch Money (a personal finance management system), it does not move money or create financial obligations—it merely updates transaction categorization metadata. This is a Write operation (modifies data reversibly).
From the tool's definition Tool description states it assigns a category to a transaction, modifying transaction metadata. This is a reversible modification operation similar to the sibling tool 'bulk_categorize_transactions' on the same financial management server.
Documented attack patterns abuse exactly the kind of access categorize_transaction gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Monarch, and nothing reaches the server without passing your rules. This is the rule we recommend for categorize_transaction:
{
"version": "1",
"default": "deny",
"tools": {
"categorize_transaction": {
"limits": [
{
"counter": "categorize_transaction_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}categorize_transaction 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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Assign a category to a transaction. Args: transaction_id: The ID of the transaction to categorize category_id: The category ID to assign. It is categorised as a Write tool in the Monarch MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Monarch MCP server in PolicyLayer and add a rule for categorize_transaction: 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 Monarch. Nothing to install.
categorize_transaction 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 categorize_transaction 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 categorize_transaction. 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.
categorize_transaction is provided by the Monarch MCP server (robcerda/monarch-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 50 Monarch tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
50 Monarch tools catalogued and risk-classified — across an index of 42,500+ MCP servers.