FastBill MCP by usefulapi

Tools are largely distinct resource+action pairs, and descriptions explicitly differentiate close pairs like create_invoice vs complete_invoice and list_invoices vs list_revenues vs list_expenses. Minor friction remains between list_customers/list_contacts and between list_invoices/list_recurring_invoices/list_revenues, but wording resolves it.

Every tool uses the same fastbill_ prefix plus a consistent verb_noun snake_case pattern (create_x, get_x, list_x, update_x). The only mild deviation, fastbill_set_invoice_paid, is still readable and follows the same style.

22 tools is on the heavy side but is justified by a broad domain covering customers, invoices, estimates, projects, time entries, expenses, revenues, recurring invoices, contacts and templates. Each tool maps to a real resource/action rather than filler.

Invoice lifecycle is well covered (create, complete, set paid, get, list) and customers have full create/read/update, but most other resources only offer create+list with no update or delete (articles, projects, estimates, time entries). There is also no cancel-invoice tool despite the description warning that final invoices can only be canceled, and no way to send estimates/invoices.