Read smallinvoice contacts, invoices, offers, projects and hours; create contacts and invoices. Hosted by usefulapi: connect it to Claude, ChatGPT, Cursor or any MCP client.
Turn on the smallinvoice connector, then ask in plain words. The AI picks the tools.
For small businesses and freelancers who invoice customers with smallinvoice.
The AI lists invoices by contact with number, dates, total and status, opens one with its positions, and lists the payments recorded on it.
The AI lists offers (quotes) and order confirmations by contact and opens one with its positions and totals.
The AI lists contacts (companies or persons) and opens one with its main address, all addresses and the contact persons of a company.
The AI lists projects, recorded working hours and efforts (expenses and services booked on projects), so you can see what to bill.
The AI checks the contacts first, then creates a new company contact with its main address. Nothing is sent to anyone.
Changes dataThe AI looks up the contact and the unit ids and creates an invoice. It is only created, not sent; you review it in smallinvoice.
Changes dataThe login page asks for your Client ID and Client secret.
Create the client yourself in smallinvoice: Home → Users → API V2, new client, grant type Client credentials, and tick the scopes you want to give the assistant (contact, invoice, offer, order confirmation, delivery note, catalog, configuration, project, working hours, effort, activity, cost unit). Create a client just for this connection, so you can delete it there at any time. The secret is used only to get smallinvoice access tokens and call the API on your behalf; it is never shown to anyone. Documents and contacts contain your customers' personal data.
Team and Enterprise: an Owner adds the connector for the organization first.
No Add custom MCP server option? It depends on your account or workspace settings: see OpenAI's guide.
Run this command, then run /mcp in Claude Code to log in:
Add to Cursor or add this to ~/.cursor/mcp.json:
{
"mcpServers": {
"smallinvoice": {
"url": "https://smallinvoice.usefulapi.io/mcp"
}
}
} Add to VS Code or add this to .vscode/mcp.json:
{
"servers": {
"smallinvoice": {
"type": "http",
"url": "https://smallinvoice.usefulapi.io/mcp"
}
}
} Run these commands. The second one opens the login page:
Windsurf, Cline, Zed and other MCP clients: add this URL as a remote MCP server (Streamable HTTP). The client then opens the login page in your browser.
Add only the URL. Do not add an Authorization header or an API key to the client config. The server signs you in with OAuth: the login page asks for your Client ID and Client secret. If the config has such a header, remove it: some clients then send that header instead of the login token, and every call fails with 401.
| Plan | Price | Limit |
|---|---|---|
| Free | $0 | 50 tool calls / month |
| Proper account | $9/mo · $90/yr | 10,000 tool calls / month |
| Pro+per account | $39/mo · $390/yr | 100,000 tool calls / month |
Each paid plan covers this smallinvoice server only. Ask your AI to run smallinvoice_upgrade and choose Pro or Pro+, billed monthly or yearly (it returns a Stripe Checkout link). If you already have Pro, ask to change it to Pro+. The change requires your confirmation, keeps your billing interval and charges the price difference for the rest of the period immediately. Cancel any time with smallinvoice_cancel_subscription: your paid plan continues to the end of the paid period, with no refund for the current period, and asking to resume the same plan with smallinvoice_upgrade before then undoes the cancel. Or write to [email protected].
smallinvoice_get_ownersmallinvoice_list_contactssmallinvoice_get_contactsmallinvoice_list_contact_addressessmallinvoice_list_contact_peoplesmallinvoice_list_contact_groupssmallinvoice_list_invoicessmallinvoice_get_invoicesmallinvoice_list_invoice_paymentssmallinvoice_list_offerssmallinvoice_get_offersmallinvoice_list_order_confirmationssmallinvoice_get_order_confirmationsmallinvoice_list_delivery_notessmallinvoice_get_delivery_notesmallinvoice_list_productssmallinvoice_list_servicessmallinvoice_list_unitssmallinvoice_list_bank_accountssmallinvoice_list_projectssmallinvoice_get_projectsmallinvoice_list_working_hourssmallinvoice_list_effortssmallinvoice_list_activitiessmallinvoice_list_cost_unitssmallinvoice_create_contactsmallinvoice_create_invoicesmallinvoice_usage_statussmallinvoice_request_featuresmallinvoice_upgradesmallinvoice_cancel_subscriptionCheck the invoices of a customer. Review offers and order confirmations. Find a customer or supplier. Review hours and efforts per project. Add a customer company. Create an invoice for a customer. See what you can do for the details.
No. usefulapi is an independent service. It is not affiliated with or endorsed by smallinvoice. The server calls the smallinvoice API with your own smallinvoice access, so it sees only the data that your account can see.
Yes. In Claude, add this server's URL as a custom connector. In ChatGPT, add it as a custom MCP server in Plugins. Then log in once. Cursor, VS Code, Claude Code and Codex work too. See the setup steps.
The login page asks for your Client ID and Client secret. See Before you connect for where to find them.
No. Add only the URL. Do not add an Authorization header or an API key to the client config. The server signs you in with OAuth: the login page asks for your Client ID and Client secret. If the config has such a header, remove it: some clients then send that header instead of the login token, and every call fails with 401.
The login stores them encrypted in the authorization grant of your connection. The server uses them to call the smallinvoice API for you and to derive a private account id for usage metering. usefulapi does not show them on any page or in any reply. To stop all access, remove the connector and change or delete these credentials in smallinvoice.
Yes, if you approve it. 2 of the 27 smallinvoice tools can create or change data. The other 25 are marked read-only. Most MCP clients ask you to approve a tool call before it runs.
The Free plan gives 50 tool calls / month. Pro costs $9/mo or $90/yr, with 10,000 tool calls / month. Pro+ costs $39/mo or $390/yr, with 100,000 tool calls / month. Each subscription covers this smallinvoice server only. Cancel any time: your paid plan then runs to the end of the paid period. Run smallinvoice_usage_status to see how many calls you used.
Ask the AI to run smallinvoice_upgrade and choose Pro or Pro+, billed monthly or yearly: it returns a Stripe Checkout link. If you already have Pro, ask to change it to Pro+. After you confirm, your existing subscription changes in place, keeps its billing interval and charges the price difference for the rest of the period immediately. To cancel, run smallinvoice_cancel_subscription. Your paid plan continues to the end of the paid period.
Tell the AI what you wanted to do. It can send the request with smallinvoice_request_feature. We store the text with the server name, the type of AI client and the tool you tried, not with your account, and read every request when we plan new tools. You can send up to 5 requests per day.
Any client that supports remote MCP servers (Streamable HTTP) with OAuth login: Claude (web and desktop), Claude Code, ChatGPT, Codex, Cursor, VS Code, Windsurf and others.
This is a Model Context Protocol endpoint — meant to be connected from an AI client, not opened in a browser. An invalid_token response at the URL is the auth gate working as designed; clients authenticate automatically.
Need a tool this server does not have, or a connection to another system? We build custom integrations and MCP servers.