Create a service invoice (NFS-e) in Bling
AI agents use create_service_invoice to create or update resources in Mcp Ap2 — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Mcp Ap2 environment.
The tool creates a new service invoice document in the Bling system. This is a Write operation as it creates a new record. While invoices have financial implications, this tool is generating a billing document rather than directly moving money or committing financial obligations, placing it in Write rather than Financial. Severity is medium due to the potential for fraudulent or erroneous invoice creation.
From the tool's definition "Create a service invoice (NFS-e) in Bling"
Documented attack patterns abuse exactly the kind of access create_service_invoice gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Mcp Ap2, and nothing reaches the server without passing your rules. This is the rule we recommend for create_service_invoice:
{
"version": "1",
"default": "deny",
"tools": {
"create_service_invoice": {
"limits": [
{
"counter": "create_service_invoice_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}create_service_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.
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Create a service invoice (NFS-e) in Bling. It is categorised as a Write tool in the Mcp Ap2 MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Mcp Ap2 MCP server in PolicyLayer and add a rule for create_service_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 Mcp Ap2. Nothing to install.
create_service_invoice is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the create_service_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.
Set action: deny in the PolicyLayer policy for create_service_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.
create_service_invoice is provided by the Mcp Ap2 MCP server (@codespar/mcp-ap2). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Mcp Ap2, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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