add_transaction · Finance MCP Server MCP: Risk & Policy

WHAT IT DOES

What add_transaction does on Finance MCP Server

AI agents use add_transaction to create or update resources in Finance MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Finance MCP Server environment.

WHY IT NEEDS A POLICY

Why add_transaction needs a policy

This tool creates new financial data entries reversibly. While it involves financial data, the action itself is not moving money (Financial category requires actual monetary transfers/obligations) nor is it executing arbitrary code (Execute category). The 'Add' verb and 'new transaction' language clearly indicate Write semantics.

From the tool's definition Tool description states 'Add a new income or expense transaction', which creates new data records in the SQLite storage without modification or deletion of existing records.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

add_transaction Rate-limited

add_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.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "add_transaction": {
      "limits": [
        {
          "counter": "add_transaction_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Finance MCP Server, so you can run agents against it safely.

FAQ

Questions about add_transaction

What does the add_transaction tool do? +

Add a new income or expense transaction. It is categorised as a Write tool in the Finance MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on add_transaction? +

Register the Finance MCP Server MCP server in PolicyLayer and add a rule for add_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 Finance MCP Server. Nothing to install.

What risk level is add_transaction? +

add_transaction is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit add_transaction? +

Yes. Add a rate_limit block to the add_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.

How do I block add_transaction completely? +

Set action: deny in the PolicyLayer policy for add_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.

What MCP server provides add_transaction? +

add_transaction is provided by the Finance MCP Server MCP server (taylor3lewis/finance-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.