update_transactions · Ynab MCP: Risk & Policy

WHAT IT DOES

What update_transactions does on Ynab

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

WHY IT NEEDS A POLICY

Why update_transactions needs a policy

This tool modifies existing financial transaction records in bulk. While not directly moving money, bulk-updating transactions in a budgeting system can alter financial records at scale, making misuse high severity. It is reversible in principle (records can be changed back), so Write is the appropriate category rather than Destructive or Financial.

From the tool's definition Update multiple transactions at once

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

update_transactions Rate-limited

update_transactions 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": {
    "update_transactions": {
      "limits": [
        {
          "counter": "update_transactions_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 Ynab, so you can run agents against it safely.

FAQ

Questions about update_transactions

What does the update_transactions tool do? +

[1 API call, bulk] Update multiple transactions at once. Each must include either id or import_id to identify the transaction. It is categorised as a Write tool in the Ynab MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on update_transactions? +

Register the Ynab MCP server in PolicyLayer and add a rule for update_transactions: 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 Ynab. Nothing to install.

What risk level is update_transactions? +

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

Can I rate-limit update_transactions? +

Yes. Add a rate_limit block to the update_transactions 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 update_transactions completely? +

Set action: deny in the PolicyLayer policy for update_transactions. 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 update_transactions? +

update_transactions is provided by the Ynab MCP server (justmytwospence/ynab-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.