Justworks API
Justworks publishes a versioned Partner API with OAuth 2.0, granular scopes, and well-specified webhooks covering employees, payrolls, deductions, and time off. Access is partner-gated: OAuth apps are created by emailing partner-api@justworks.com, not through self-serve signup.
Frequently asked questions
Justworks scores A+ on the API Report Card. Justworks publishes a versioned Partner API with OAuth 2.0, granular scopes, and well-specified webhooks covering employees, payrolls, deductions, and time off. Access is partner-gated: OAuth apps are created by emailing partner-api@justworks.com, not through self-serve signup.
Justworks has a workable official integration path. Most engineering teams can build against it directly. Open API: self-serve, documented, with SDKs
Justworks is a modern Professional Employer Organization (PEO) and payroll platform for small and mid-sized U.S. businesses.
Vertical: Enterprise / HR / ERP (PEO + SMB payroll). Running semi-monthly and off-cycle payroll runs with automatic federal, state, and local tax filing. Onboarding new W-2 hires (offer letters, I-9, W-4, direct deposit).
7/10. Justworks serves approximately 10,000+ small business customers and several hundred thousand W-2 employees, making it one of the largest modern PEOs in the U.S. alongside TriNet, Insperity, ADP TotalSource, and Paychex PEO.
Justworks holds extraordinarily sensitive operating data as the employer of record under the PEO co-employment model. This includes: Employee PII (SSN/tax IDs, DOB, home address, contact info). Bank/ACH details for direct deposit and ACH transaction history.
Founded in 2012 (~14 years old as of 2026). Cloud-native, modern React-based UI, mobile-friendly employee app, transparent online pricing, and a published OAuth 2.0 Partner API with HMAC-signed webhooks, all hallmarks of a modern, developer-aware platform.
Grades measure one thing: can a customer's engineering team get their own data out programmatically? We check six things (whether a real API exists, how access is gated, data coverage, auth quality, docs and developer experience, and stability) and roll them into a letter grade. Grades get re-verified, and they only move on evidence.