FastEndpoints is a focused ASP.NET Core API framework optimized for REPR-pattern endpoints; CleenUI is a complete full-stack codebase including the API layer.
FastEndpoints is a focused open-source API framework that replaces ASP.NET Core's default controller model with a REPR-style (Request, Endpoint, Response) endpoint-per-class pattern. It's a great choice for teams who want a more opinionated API library on top of ASP.NET Core. ⚠️ As of mid-2026, the FastEndpoints maintainer announced on the project homepage that the library is moving to 'bugfix-only mode' due to insufficient sponsorship — new features are paused indefinitely. Teams starting greenfield projects should factor open-source sustainability into their vendor evaluation. CleenUI is a complete full-stack codebase — the API layer is one of four tiers shipping in the box, alongside the database, the frontend, and the background services. CleenUI uses standard ASP.NET Core Web API controllers (not REPR-pattern), and has no OSS funding dependency.
| Category | CleenUI | FastEndpoints |
|---|---|---|
| Scope | Full-stack — API + database + frontend + background services + 15 modules | API library only — you build everything else |
| Distribution model | Licensed source code (one-time license) | Open-source NuGet package (MIT) |
| API style | Standard ASP.NET Core Web API controllers | REPR pattern (Request → Endpoint → Response) |
| Frontend | React 18 SPA with 61 components | Not included — bring your own |
| Database layer | Azure SQL + Dapper + ADO.NET + 300+ tables + 700+ stored procedures (no EF) | Not included — bring your own ORM |
| Auth / RBAC | Auth0 + JWT wired end-to-end with RBAC + row-level scoping | Validators + auth handlers; you wire identity |
| Pricing model | Custom-scoped engagement | Free |
| OSS sustainability risk | No OSS funding dependency — licensed source code, not a framework | ⚠️ Announced bugfix-only mode (mid-2026) — new features paused due to low sponsorship |
Pick FastEndpoints when you specifically need a different API pattern than ASP.NET Core controllers and you're building the rest of the stack yourself.
Pick CleenUI when you want the entire stack — not just the API layer — and you'd rather not assemble four open-source libraries plus a frontend plus a database design.