Read FastBill customers, invoices, estimates, expenses; create customers, invoices, projects. Hosted by usefulapi: connect it to Claude, ChatGPT, Cursor or any MCP client.
Turn on the FastBill connector, then ask in plain words. The AI picks the tools.
For freelancers and small businesses that keep their invoicing and bookkeeping in FastBill.
The AI lists invoices by state and due date, with customer, totals and line items, so you can see what to chase.
The AI finds or creates the customer and creates a draft invoice from line items. The invoice stays a draft and is not sent.
Changes dataAfter you confirm the draft, the AI finalizes it so it gets an invoice number. A final invoice can no longer be edited in FastBill.
Changes dataThe AI marks a final invoice as paid with the payment date and method once the money has arrived.
Changes dataThe AI lists your projects and books a time entry with customer, project and start time, and later reads the entries back.
Changes dataThe AI lists the expense and revenue entries of a date range, so you can compare income and costs before the tax advisor asks.
The login page asks for your FastBill login e-mail address and FastBill API key.
Find the API key in FastBill under Einstellungen (Settings) → Integrationen / API. The e-mail address is the one you log in to FastBill with. FastBill limits API calls per hour by plan (Solo 50, Solo-Plus 100, Pro 500, Premium 1000), so every tool call counts against it. Your key is used only to call the FastBill API on your behalf; it is never shown to anyone.
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": {
"fastbill": {
"url": "https://fastbill.usefulapi.io/mcp"
}
}
} Add to VS Code or add this to .vscode/mcp.json:
{
"servers": {
"fastbill": {
"type": "http",
"url": "https://fastbill.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 FastBill login e-mail address and FastBill API key. 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 FastBill server only. Ask your AI to run fastbill_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 fastbill_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 fastbill_upgrade before then undoes the cancel. Or write to [email protected].
fastbill_list_customersfastbill_get_customerfastbill_list_contactsfastbill_list_invoicesfastbill_get_invoicefastbill_list_recurring_invoicesfastbill_list_estimatesfastbill_list_expensesfastbill_list_revenuesfastbill_list_articlesfastbill_list_projectsfastbill_list_time_entriesfastbill_list_templatesfastbill_create_customerfastbill_update_customerfastbill_create_invoicefastbill_complete_invoicefastbill_set_invoice_paidfastbill_create_estimatefastbill_create_articlefastbill_create_projectfastbill_create_time_entryfastbill_usage_statusfastbill_request_featurefastbill_upgradefastbill_cancel_subscriptionFind overdue invoices and who owes them. Draft an invoice from a job. Finalize a checked draft. Record a payment. Log billable time on a project. Review last month's expenses and revenue. See what you can do for the details.
No. usefulapi is an independent service. It is not affiliated with or endorsed by FastBill. The server calls the FastBill API with your own FastBill 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 FastBill login e-mail address and FastBill API key. 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 FastBill login e-mail address and FastBill API key. 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 FastBill 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 FastBill.
Yes, if you approve it. 9 of the 22 FastBill tools can create or change data. The other 13 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 FastBill server only. Cancel any time: your paid plan then runs to the end of the paid period. Run fastbill_usage_status to see how many calls you used.
Ask the AI to run fastbill_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 fastbill_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 fastbill_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.