What is SimpleW?

SimpleW is a .NET Core library designed for building fast and secure web applications.

Just want to try it out? Skip to the Quickstart.

Architecture

SimpleW’s architecture and motivations behind its core design choices :

• Pure C# (100% managed code), running on .NET 8 or later.
• Built on top of native sockets, low latency.
• Compiled delegate, close to hard-coded method calls.
• Custom parser, low memory.
• Cross‑platform support, Windows/Linux/Android/MacOS.
• NuGet package available, easy to integrate

Use Cases

• High‑Performance

When network efficiency and observability are critical, SimpleW ensures fast request throughput and low latency. Coupled with automatic OpenTelemetry instrumentation, you gain full visibility into request flows, latency, and error rates—enabling you to scale horizontally with confidence.

• Rapid API Prototype

When you need to deliver a proof‑of‑concept API in record time, SimpleW excels. Its minimal configuration lets you define endpoints in just a few lines of code. With JSON serialization handled automatically and no heavyweight server plumbing to configure, developers can focus on business logic from the very first compile.

• Embedded Service

When resources are constrained, SimpleW’s tiny memory footprint and makes it ideal for lightweight background services, command‑and‑control agents, or any situation where simplicity and reliability are paramount.

• static site

Need to ship a single‑page app or docs alongside your API? With SimpleW you point to a folder (e.g. wwwroot), mount it under a URL, and in milliseconds all your files are served with caching—no heavy framework required. Fast, lean, and ready for your Vue.js dashboard or static site...

Why this library ?

I believe modern web application architecture should be built around a REST API acting as a clear contract between two independent parts.

The Contract Model

• Backend (single) — The backend is free to evolve, refactor, or even change language (C#, Go, Rust, PHP…). Its only obligation is to provide and respect the REST API contract.

• Frontend (one or many) — Frontends are also free to evolve independently (SPA, mobile apps, desktop clients…). They must consume and respect the same REST API contract.

This separation enforces :

• clear boundaries
• independent evolution
• long-term maintainability

My needs

Frontend :

• I mostly build fronteds as SPAs using Vite, Vue and Vuetify.
• The frontend is a separate project, compiled independently and deployed as static assets.

Backend :

• Written in C#, the language I 😍.
• Easy to integrate, lightweight, with a minimal footprint
• Focused on API serving, not full-stack rendering
• Built-in support for : routing, webSockets, server-sent events (SSE)
• No template engine required
• Ability to serve static files (typically the output of npm run build)
• Basic observability: request tracing, performance monitoring

The existings projects

I evaluated and used several existing projects over the years.

• ASP.NET Core :
  • too many features I don't need, I don't want (Razor, Blazor...).
  • some behaviors are unnecessarily complex to customize
  • heavy for small or focused APIs
• IIS an old « usine à gaz » on Windows, Kestrel and SignalR feel similarly heavy on Linux.
• EmbedIO : long-time v2 user, the v3 rewrite didn’t fit my expectations. Moreover, it relies on the old Microsoft HttpListener and the websocket-sharp alternative was not perfect.
• GenHttp : feels promising but I was in the process of writting my own.
• NetCoreServer : Fast, simple, extremly well design, and extendable. Until the v16.0.1, SimpleW was a project on top of the NetCoreServer's OnReceivedRequest()

This project

SimpleW is the result of years of experimentation, production usage, and frustration with existing solutions.

It is a web server designed to be :

• Lightweight
• Explicit
• Fast
• Easy to embed
• Focused on APIs, not full-stack magic

After 4 years in production, SimpleW now :

• Powers multiple APIs
• Handles real-world traffic reliably
• Continues to gain useful features
• Remains simple and predictable

No magic. No bloat. Just what is needed.

Final Words

SimpleW exists because I needed a server that :

• Matches my architectural beliefs
• Stays out of my way
• Scales without becoming complex

If you find a bug, have an idea, or a missing feature — feel free to open an issue.

SimpleW is opinionated, but open.