Falco + OpenAPI + Scalar

August 02, 2025 163 words One minute

Contents

This post describes an ASP.NET project template using F#, Falco, Falco.OpenApi, Swashbuckle, and Scalar.

Create an empty ASP.NET web project

dotnet new web -lang F# -o MyApp

Install nuget packages

cd MyApp
dotnet add package Falco
dotnet add package Falco.OpenApi
dotnet add package Swashbuckle.AspNetCore.SwaggerGen
dotnet add package Scalar.AspNetCore

Program.fs

open Microsoft.AspNetCore.Builder
open Microsoft.Extensions.DependencyInjection
open Microsoft.OpenApi.Models
open Falco
open Falco.Routing
open Falco.OpenApi
open Scalar.AspNetCore

[<EntryPoint>]
let main args =
    let builder = WebApplication.CreateBuilder(args)
    let appName = builder.Environment.ApplicationName
    let version = "v0.0.1"

    builder.Services
        .AddFalcoOpenApi()
        .AddSwaggerGen(_.SwaggerDoc(
            version,
            OpenApiInfo(Title = appName, Version = version, Description = "description")
        ))
    |> ignore

    let app = builder.Build()

    app.UseSwagger(fun o -> o.RouteTemplate <- "/openapi/{documentName}.json")
    |> ignore

    app.MapScalarApiReference("/docs", fun o ->
        o.AddDocument(version).WithTitle(appName) |> ignore
    ) |> ignore

    let endpoints = [
        get "/ping" (Response.ofPlainText "Hello World")
            |> OpenApi.tags [ "Main" ]
            |> OpenApi.summary "Ping"
            |> OpenApi.description "Just ping"
            |> OpenApi.returnType typeof<string>
    ]

    app.UseRouting()
        .UseFalco(endpoints)
        .Run(Response.withStatusCode 404 >> Response.ofPlainText "Not found")

    0

Result

Run the project and find the Scalar page at {baseUrl}/docs.