Suave is a simple web development F# library providing a lightweight web server and a set of combinators to manipulate route flow and task composition.

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Suave is a lightweight, non-blocking web server. The non-blocking I/O model is efficient and suitable for building fast, scalable network applications. In fact, Suave is written in a completely non-blocking fashion throughout. Suave runs on Linux, OS X and Windows flawlessly.

Suave is inspired in the simplicity of Happstack and born out of the necessity of embedding web server capabilities in my own applications. Still in its early stages Suave supports HTTPS, multiple TCP/IP bindings, Basic Access Authentication, Keep-Alive and HTTP compression.


To install Suave, add the following to your paket.dependencies:

nuget Suave

Or you can use the legacy NuGet command line Package Manager Console:

PM> Install-Package Suave

The simplest possible application: Hello World!

The simplest Suave application is a simple HTTP server that greets all visitors with the string "Hello World!"

open Suave

startWebServer defaultConfig (Successful.OK "Hello World!")

The above statement will start a web server on default port 8080 over HTTP. startWebServer takes a configuration record and the WebPart (OK "Hello World") It’s worth noting that with the above, your application will block on the function call, until you cancel the Async.DefaultCancellationToken. If you want to handle disposal of the async yourself, have a look at startWebServerAsync.


To test the above yourself, paste that code in Hello.fsx and then invoke it with fsharpi Hello.fsx (or fsi Hello.fsx on Windows). Completely new? Here are installation instructions on OS X/macOS, Windows and Linux. If you have Visual Studio installed you should be able to find the “F# Interactive” in your menus.

If you are running in an IDE, and not starting Suave via Hello.fsx, you’ll want to provide a way of stopping the server without having to restart the IDE; the code below will run the server until a key is pressed in the console window, then shuts down the server.

open System
open System.Threading
open Suave

let main argv = 
  let cts = new CancellationTokenSource()
  let conf = { defaultConfig with cancellationToken = cts.Token }
  let listening, server = startWebServerAsync conf (Successful.OK "Hello World")
  Async.Start(server, cts.Token)
  printfn "Make requests now"
  Console.ReadKey true |> ignore

  0 // return an integer exit code

In suave, we have opted to write a lot of documentation inside the code; so just hover the function in your IDE or use an assembly browser to bring out the XML docs. You can also browse our API reference.