Read FastBill customers, invoices, estimates, expenses; create customers, invoices, projects. For freelancers and small businesses that keep their invoicing and bookkeeping in FastBill. Hosted by usefulapi — connect from Claude, ChatGPT, Cursor, or any MCP client.
Team and Enterprise: an Owner adds the connector for the organization first.
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"
}
}
}No Add custom MCP server option? It depends on your account or workspace settings: see OpenAI's guide.
Run these commands. The second one opens the login page:
Other MCP clients (Windsurf, Cline, Zed and more): add the URL as a remote MCP server (Streamable HTTP). The client then opens the login page in your browser. Do not add an Authorization header: see Before you connect.
The AI lists invoices by state and due date, with customer, totals and line items, so you can see what to chase.
fastbill_list_invoices fastbill_get_customer
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 data · fastbill_list_customers fastbill_create_customer fastbill_create_invoice
After 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 data · fastbill_get_invoice fastbill_complete_invoice
The AI marks a final invoice as paid with the payment date and method once the money has arrived.
Changes data · fastbill_list_invoices fastbill_set_invoice_paid
The AI lists your projects and books a time entry with customer, project and start time, and later reads the entries back.
Changes data · fastbill_list_projects fastbill_create_time_entry fastbill_list_time_entries
The AI lists the expense and revenue entries of a date range, so you can compare income and costs before the tax advisor asks.
fastbill_list_expenses fastbill_list_revenues
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.
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.
Turn on the FastBill connector, then ask in plain words. The AI picks the tools.
| Tool | Type | What it does |
|---|---|---|
fastbill_list_customers | read | List customers List customers (name, address, e-mail, VAT id, payment terms and bank details as stored in FastBill). Filter by search term (organization, name, address, zip, e-mail or tags), customer number, country or city. customer.get. |
fastbill_get_customer | read | Get customer One customer by FastBill customer id. customer.get with CUSTOMER_ID. |
fastbill_list_contacts | read | List contacts List contact persons of customers (name, position, e-mail, phone). Filter by customer, search term or contact id. contact.get. |
fastbill_list_invoices | read | List invoices List outgoing invoices, drafts and credit notes with totals, state (draft, unpaid, overdue, paid, canceled), dates and line items. Filter by customer, number, type, date ranges (invoice date, due date, paid date, last update). invoice.get. |
fastbill_get_invoice | read | Get invoice One invoice by FastBill invoice id, with all line items, VAT, payments and the document URL. invoice.get with INVOICE_ID. |
fastbill_list_recurring_invoices | read | List recurring invoices List recurring invoice templates (customer, interval data, totals, items). recurring.get. |
fastbill_list_estimates | read | List estimates List estimates (quotes) with state (a created, b sent, c negotiation, d accepted, e rejected, f invoiced), totals and items. estimate.get. |
fastbill_list_expenses | read | List expenses List expense entries (supplier, category, net/VAT/gross, dates, document URL). Filter by invoice number or date ranges. expense.get. |
fastbill_list_revenues | read | List revenues List revenue entries (income booked in FastBill: customer, totals, dates, payments). Takes the same filters as invoices. revenue.get. |
fastbill_list_articles | read | List products List products and services (article number, type, title, unit price, VAT, unit). article.get. |
fastbill_list_projects | read | List projects List projects (name, customer, hourly rate, VAT, start/end date). project.get. |
fastbill_list_time_entries | read | List time entries List work time entries (customer, project, date, minutes, billable minutes, comment, invoice). Without filters FastBill returns the latest entries of the current month. time.get. |
fastbill_list_templates | read | List document templates List the invoice/estimate templates (template id, name, hash). Use a template id with the create tools. Ids change whenever a template is edited. template.get. |
fastbill_create_customer | write | Create customer WRITE: create a customer. customer_type is required; a business needs organization, a consumer needs last_name. Bank details are not accepted by this tool. FastBill does not check for duplicates, so search with fastbill_list_customers first. customer.create. |
fastbill_update_customer | write | Update customer WRITE: update fields of an existing customer; only the fields you pass change. Bank details are not accepted by this tool. customer.update. |
fastbill_create_invoice | write | Create invoice WRITE: create an invoice for a customer from line items. FastBill stores it as a draft; it gets its number and becomes final only with fastbill_complete_invoice, and it is never sent by this tool. Check the result with fastbill_get_invoice. invoice.create. |
fastbill_complete_invoice | write | Finalize invoice WRITE, NOT REVERSIBLE: turn a draft invoice into a final invoice. FastBill assigns the invoice number and PDF; a final invoice can no longer be edited (it can only be canceled in FastBill). Nothing is sent to the customer. Only call this after the user confirmed the draft. invoice.complete. |
fastbill_set_invoice_paid | write | Mark invoice paid WRITE: mark a final invoice as paid, with the payment date and method. invoice.setpaid. |
fastbill_create_estimate | write | Create estimate WRITE: create an estimate (quote) for a customer from line items. It is not sent. estimate.create. |
fastbill_create_article | write | Create product WRITE: create a product or service (article number, title and unit price are required). article.create. |
fastbill_create_project | write | Create project WRITE: create a project for a customer (name and customer are required). project.create. |
fastbill_create_time_entry | write | Create time entry WRITE: book a work time entry on a project (customer, project and start time are required). time.create. |
fastbill_usage_status | Usage status (free-tier meter) Report the caller's current usage: the plan, calls used this month, the limit of the plan (the free monthly cap or the Pro fair use limit), remaining, and whether the limit is reached. Read-only; does not count against the meter. | |
fastbill_request_feature | Request a missing feature Tell usefulapi that the user needs something the FastBill tools cannot do yet (a missing tool, field or filter). Call it only when the user asks for something none of the tools can do, and tell the user that you send the request. Do not call it for errors or for normal requests. Do not include personal data, credentials or customer records. Stored with the product name and the client type (for example Claude or Cursor), without the user's account. At most 5 requests per day. Does not count against the meter. | |
fastbill_upgrade | Upgrade to Pro (unlimited*) Get Pro: unlimited tool calls (fair use limit: 10,000 a month) on FastBill (the free tier caps monthly usage). Plans: "monthly" — $9/month; "yearly" — $90/year (2 months free). Cancel any time: Pro then runs to the end of the paid period, so it also suits a one-time job. *A fair use limit applies. For heavy use (near Pro's limit): "plus" or "plus_yearly" — Pro+, $39/month or $390/year, unlimited tool calls (fair use limit: 100,000 a month); an existing Pro subscription changes to Pro+ in place (needs confirm: true; the price difference for the rest of the period is charged at once). Otherwise returns a short link to open in your browser (it opens Stripe Checkout); after payment the account upgrades automatically. Does not count against the meter. | |
fastbill_cancel_subscription | Cancel the Pro subscription Cancel the caller's FastBill Pro subscription at the end of the paid period (no refund for the current period; Pro continues until then, then the free tier applies). Requires confirm: true. Run fastbill_upgrade later to undo the cancel before the period ends. Does not count against the meter. |
| Plan | Price | Limit |
|---|---|---|
| Free | $0 | 50 tool calls / month |
| Proper account | $9/mo · $90/yr | Unlimited* |
*Pro fair use limit: 10,000 tool calls a month on this server. For more, write to [email protected].
Pro covers this FastBill server only. Subscribe with fastbill_upgrade (it returns a Stripe Checkout link). Cancel any time with fastbill_cancel_subscription: Pro continues to the end of the paid period, with no refund for the current period, and running fastbill_upgrade before then undoes the cancel. Or write to [email protected].
Find 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 unlimited tool calls (fair use limit: 10,000 tool calls a month), for this FastBill server only. Cancel any time: Pro 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: it returns a Stripe Checkout link. To cancel, run fastbill_cancel_subscription. Pro 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.