Invoice clients for REST/GraphQL API development, third-party integrations, and API documentation. Professional invoices from Tidybill.
An API developer invoice covers work designing, building, and documenting application programming interfaces that allow different software systems to communicate. API developers build REST or GraphQL APIs, integrate third-party services (payment gateways, CRMs, shipping APIs), implement webhook systems, and create the data interchange layer that powers modern software. API work is a common component of larger software projects, but it is also frequently commissioned as a standalone engagement when a business needs to expose its data to partners, build an integration with a third-party platform, or create a backend for a mobile app. Invoices should describe the specific endpoints or integrations built, the authentication mechanism implemented, and any documentation produced. API documentation (OpenAPI/Swagger specs) is a distinct billable deliverable.
| Service | Typical Rate | Unit |
|---|---|---|
| API development (hourly) | 75 | hour |
| REST API build | 2000 | project |
| Third-party API integration | 600 | integration |
| GraphQL API development | 2500 | project |
| API documentation (OpenAPI spec) | 500 | project |
| Webhook implementation and testing | 400 | project |
For API builds, invoice on completion of agreed endpoint set. For large API projects, invoice at milestones: authentication and core CRUD endpoints, business logic endpoints, integrations, documentation and testing complete. List each integration as a separate line item with the third-party service named. Include API documentation as a separate deliverable with its own line item so clients value it appropriately.