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smallinvoice MCP by usefulapi

io.usefulapi/smallinvoice in the official MCP registry. Endpoint https://smallinvoice.usefulapi.io/mcp. Source: github.com/m190/usefulapi-mcp.

The registry describes it as: Read smallinvoice contacts, invoices, offers, projects and hours; create contacts and invoices.

We read its 27 tools on 2026-10-31. Nothing in them matched our tool-poisoning rules. It also sets server instructions, text a client puts in front of the model on connect; those were read too.

A clean read means these rules found nothing, not that the server is harmless. A server can change its tools at any time, which is why the index reads it again every week.

Connect it

The endpoint answers MCP over HTTP; that is how we read it. Add it to your client:

Claude Code

claude mcp add --transport http smallinvoice https://smallinvoice.usefulapi.io/mcp

Cursor: ~/.cursor/mcp.json

{
  "mcpServers": {
    "smallinvoice": {
      "url": "https://smallinvoice.usefulapi.io/mcp"
    }
  }
}

VS Code

code --add-mcp '{"name":"smallinvoice","type":"http","url":"https://smallinvoice.usefulapi.io/mcp"}'

Some servers ask you to sign in the first time a client connects, or want a key from the people who run them; the server's own docs say which.

Let Claude Code check servers as it adds them

With the free lazaretto-guard plugin installed, when Claude Code adds a server for you or writes one into an MCP config, the plugin reads the server's tools first and asks you if one of our rules matches. Install it, restart Claude Code, then ask it to run the command above.

Install lazaretto-guard

claude plugin marketplace add jamesdfinance-dev/lazaretto-plugins
claude plugin install lazaretto-guard@lazaretto-plugins

Tools it advertises

smallinvoice_get_owner smallinvoice_list_contacts smallinvoice_get_contact smallinvoice_list_contact_addresses smallinvoice_list_contact_people smallinvoice_list_contact_groups smallinvoice_list_invoices smallinvoice_get_invoice smallinvoice_list_invoice_payments smallinvoice_list_offers smallinvoice_get_offer smallinvoice_list_order_confirmations smallinvoice_get_order_confirmation smallinvoice_list_delivery_notes smallinvoice_get_delivery_note smallinvoice_list_products smallinvoice_list_services smallinvoice_list_units smallinvoice_list_bank_accounts smallinvoice_list_projects smallinvoice_get_project smallinvoice_list_working_hours smallinvoice_list_efforts smallinvoice_list_activities smallinvoice_list_cost_units smallinvoice_create_contact smallinvoice_create_invoice

Tool changes

We compare every full read of this server with the one before. No change in what its tools say has been seen since we started keeping this record on 2026-10-30.

Fingerprint of its tools at our last full read (2026-10-31): a077fd3584d090bc. A client can hash the tools it is served the same way and compare; the full value and a hash per tool are in this page as JSON.

Run this server? Show the check in your README

The badge reflects the latest weekly read:

Markdown

[![MCP tool check](https://lazaretto.dev/mcp-registry/io-usefulapi-smallinvoice/badge.svg)](https://lazaretto.dev/mcp-registry/io-usefulapi-smallinvoice)

How this was checked

Lazaretto connects to the endpoint the way any MCP client does, asks the server to introduce itself and list its tools, and reads every name, description, parameter schema and server instruction for tool poisoning: hidden directive blocks, orders to read local secrets, parameters built to carry secrets or the conversation out, orders that redirect another server's tools, and invisible characters. It never calls a tool. What we found across the registry.

To run the same check every time Claude Code adds a server, install the free lazaretto-guard plugin. Browse every server in the index.