The Moonworkers Payroll API is a REST API that lets software developers run complete UK payroll inside their own products: payroll calculation, payslips and documents, and HMRC submissions. The full reference is at https://payroll-api.moonworkers.co.uk/api/redoc/.
What does the API cover?
The whole payroll cycle, with nothing available only in the app. It calculates PAYE income tax, employee and employer National Insurance (including directors on the annual or alternative method), Construction Industry Scheme deductions, zero-hours and irregular-hours workers, and all statutory payments (SSP, SMP, SPP, SAP, ShPP, SPBP, neonatal care pay). See "Which parts of the payroll process does the API cover?".
How are HMRC submissions made?
Through Moonworkers' HMRC recognition, so you do not need your own. Your integration creates the FPS for each payrun and submits it, sends the EPS when there is something to report, and handles CIS300 returns and subcontractor verification. Notices HMRC sends back through the Data Provisioning Service (tax codes, student loans) arrive through the API too. See "Do we need our own HMRC recognition to file through the Payroll API?".
Can one integration serve many employers?
Yes. One set of credentials covers as many employers and PAYE schemes as you need, each with its own pay schedules running at once. This is built for bureaux, accountancy platforms and workforce tools. See "Is the Payroll API built for multi-tenant or bureau use?".
Which documents does it produce?
Payslips, P45, P60, P11D, P30, P32 and CIS statements, as PDFs through the API.
How do I get access?
The sandbox is free, with no approval step: request a key at https://www.moonworkers.co.uk/api and the credentials arrive by email. See "How do I get a Payroll API sandbox key?" and "Authenticating with the Payroll API".
How is it priced?
Per payslip, on volume bands, with no minimum commitment. See "Payroll API pricing: per payslip, not per employee".
What service level applies?
Production accounts are covered by a 99.9% uptime SLA. Enterprise terms are available on request.