create_voucher · Fortnox MCP: Risk & Policy

WHAT IT DOES

What create_voucher does on Fortnox

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

WHY IT NEEDS A POLICY

Why create_voucher needs a policy

This tool creates accounting records that modify financial data in Fortnox's accounting platform. While it does not move money directly (Financial category), it creates irreversible or difficult-to-audit journal entries that affect the organization's ledger and financial statements.

From the tool's definition Tool creates a manual journal entry (voucher) in an accounting system. Description states 'Create a manual journal entry (voucher)' with double-entry accounting constraints (debit = credit balance requirement).

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

create_voucher Rate-limited

create_voucher 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": {
    "create_voucher": {
      "limits": [
        {
          "counter": "create_voucher_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 Fortnox, so you can run agents against it safely.

FAQ

Questions about create_voucher

What does the create_voucher tool do? +

Create a manual journal entry (voucher). Rows must balance (total debit = total credit). It is categorised as a Write tool in the Fortnox MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on create_voucher? +

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

What risk level is create_voucher? +

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

Can I rate-limit create_voucher? +

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

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

create_voucher is provided by the Fortnox MCP server (proviscale/fortnox-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.