Payroll API: Overview
The Moonworkers Payroll API is a REST API that allows software developers to embed UK payroll calculations into their
own applications. It is available to both sandbox and production environments.
Full API reference documentation is available at payroll-api.moonworkers.co.uk/api/redoc/
What the API covers
The API provides a complete UK payroll calculation engine. It handles PAYE income tax, employee and employer National
Insurance contributions (including directors' NI on the annual earnings period method), Construction Industry Scheme
(CIS) deductions, zero-hours and irregular-hours workers, and all statutory payment types (SMP, SSP, SPP, SAP, ShPP).
RTI submissions are triggered automatically on each payroll run. The API sends Full Payment Submissions (FPS) to HMRC
and Employer Payment Summaries (EPS) at the appropriate times, with no additional action required from the developer.
Multiple employers and pay schedules
A single API integration can manage multiple employer PAYE schemes. Each employer can have multiple pay schedules
running concurrently (weekly, fortnightly, four-weekly, or monthly). This is designed for payroll bureaus, accountancy
platforms, and workforce management tools that process payroll on behalf of multiple clients.
HMRC document generation
The API generates the following documents as PDFs via API response: payslips, P60 (end of year certificates), P45
(employee leaving documents), P11D (benefits in kind), and CIS300 monthly returns for subcontractor schemes.
Sandbox access
The sandbox environment is available without approval. You can test the full API including payroll calculations and
document generation without connecting to HMRC live systems. Production access requires approval and is subject to
per-payslip or per-submission pricing with no minimum commitment.
SLA
Production accounts are covered by a 99.9% uptime SLA. Enterprise SLA terms are available on request.
