firefly_update_transaction · Firefly III MCP Server MCP

WHAT IT DOES

What firefly_update_transaction does on Firefly III MCP Server

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

WHY IT NEEDS A POLICY

Why firefly_update_transaction needs a policy

This tool modifies financial records reversibly (transactions can be updated multiple times or corrected), making it a Write operation rather than Destructive. However, it carries high severity because misuse could alter financial records, create audit trail issues, or record fraudulent transactions.

From the tool's definition Tool description explicitly states 'Update an existing transaction' and operates on financial data within Firefly III personal finance software.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

firefly_update_transaction Rate-limited

firefly_update_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": {
    "firefly_update_transaction": {
      "limits": [
        {
          "counter": "firefly_update_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 Firefly III MCP Server, so you can run agents against it safely.

FAQ

Questions about firefly_update_transaction

What does the firefly_update_transaction tool do? +

Update an existing transaction. Only provide the fields you want to change. First use firefly_get_transaction to retrieve the current values, then pass only the changed fields here. It is categorised as a Write tool in the Firefly III 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 firefly_update_transaction? +

Register the Firefly III MCP Server MCP server in PolicyLayer and add a rule for firefly_update_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 Firefly III MCP Server. Nothing to install.

What risk level is firefly_update_transaction? +

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

Can I rate-limit firefly_update_transaction? +

Yes. Add a rate_limit block to the firefly_update_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 firefly_update_transaction completely? +

Set action: deny in the PolicyLayer policy for firefly_update_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 firefly_update_transaction? +

firefly_update_transaction is provided by the Firefly III MCP Server MCP server (przbadu/firefly-iii-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.