xero_attach_file_to_invoice · Xero Expenses MCP

WHAT IT DOES

What xero_attach_file_to_invoice does on Xero Expenses MCP

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

WHY IT NEEDS A POLICY

Why xero_attach_file_to_invoice needs a policy

Attaching a file to an invoice is a Write operation: it modifies existing data (the invoice record) by adding metadata/attachments, but the change is reversible (the file can be removed). This is less severe than Destructive (which cannot be undone) and does not execute arbitrary code or move money.

From the tool's definition Tool description states 'Attach a file (PDF, image) to an existing Xero invoice' — this modifies an invoice by adding a file attachment, a reversible operation.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

xero_attach_file_to_invoice Rate-limited

xero_attach_file_to_invoice 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": {
    "xero_attach_file_to_invoice": {
      "limits": [
        {
          "counter": "xero_attach_file_to_invoice_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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Instant setup, no code required.

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

FAQ

Questions about xero_attach_file_to_invoice

What does the xero_attach_file_to_invoice tool do? +

Attach a file (PDF, image) to an existing Xero invoice. It is categorised as a Write tool in the Xero Expenses MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on xero_attach_file_to_invoice? +

Register the Xero Expenses MCP server in PolicyLayer and add a rule for xero_attach_file_to_invoice: 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 Xero Expenses MCP. Nothing to install.

What risk level is xero_attach_file_to_invoice? +

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

Can I rate-limit xero_attach_file_to_invoice? +

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

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

xero_attach_file_to_invoice is provided by the Xero Expenses MCP server (muness/xero-expenses-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.