Create invoices, manage clients, track expenses, and run estimates programmatically. The Billbooks public API covers invoices, estimates, clients, items, and expenses, with the same logic that powers the app itself: real stock deduction, real client-balance reconciliation, not a stubbed subset.
The Billbooks API is a bearer-token REST API scoped to your organization. It covers five resources, invoices, estimates, clients, items, and expenses, each with full create, read, update, and delete support. Every account can generate a key from Settings without contacting anyone, and every response follows one consistent JSON shape. Full reference docs, guides, and a quickstart live at docs.billbooks.com.
Invoices
Create and send invoices with real stock deduction and client-balance updates, not a simplified copy.
Estimates
Send quotes to clients before you invoice, using the same catalog and line-item rules.
Clients
Look up, create, and update the client list every invoice and estimate is scoped to.
Items
Maintain a catalog of billable items and services, with optional stock tracking on physical goods.
Expenses
Log expenses and link them to the invoices that bill them back to a client.
Generate an API key
From inside your Billbooks account, Settings, API Keys. No separate developer portal or signup.
Make your first call
Follow the quickstart to create a client, then send them an invoice, in about five minutes.
Build against real docs
Every endpoint, field, and error code is documented from the actual API spec, plus guides for the parts that are not obvious from the reference alone: stock deduction, expense linking, delete guard rails.
curl -X POST https://app.billbooks.com/api/public-api/v1/invoices \
-H "Authorization: Bearer bb_live_your_key_here" \
-H "Content-Type: application/json" \
-d '{
"client_id": 4821,
"date": "2026-08-18",
"no": "INV-1042",
"status": "sent",
"items": [{ "description": "Design work", "qty": 1, "rate": 1500 }]
}'Beyond the REST API, we are building one-click integrations and connectors so Billbooks slots straight into the tools you already run. Zapier, Shopify, WooCommerce, and many more are on the way, so keeping your billing in sync is one less thing to worry about.
This API does not have webhooks yet, so if your integration needs to react to events, poll the relevant endpoint. Rate limits apply per resource independently at 300 requests per 5 minutes. Full details on both, along with authentication, error handling, and every field on every resource, are in the docs.
Every endpoint, every field, every error code, documented straight from the API spec.
Read the docsSee also: Pricing, Invoicing, Quotes & Estimates, and Free Tools.