A super-simple web server framework


Version on this page:1.0.1
LTS Haskell 20.26:1.1.1
Stackage Nightly 2022-11-17:1.1.0
Latest on Hackage:1.1.1

See all snapshots webby appears in

Apache-2.0 licensed
This version can be pinned in stack with:webby-1.0.1@sha256:5d4eea45a6459de9f57914f0540da57fd94a9c157889f058f5e09c7ebca97a72,2947

Module documentation for 1.0.1


An easy to use Haskell web-server inspired by Scotty.


Clone the repo and run stack build


module Main where

import qualified Network.Wai.Handler.Warp as W
import qualified Network.Wai              as W
import           Network.HTTP.Types       (status500)

import           UnliftIO                 (liftIO)
import qualified UnliftIO.Exception       as E

import           Relude                   hiding (get, put)
import           Relude.Print             (putTextLn)
import qualified Data.Text                as T

import           Webby

-- An example exception handler web-applications can install with webby
appExceptionHandler :: T.Text -> (E.SomeException -> WebbyM appEnv ())
appExceptionHandler appName = \(exception :: E.SomeException) -> do
    setStatus status500
    let msg = appName <> " failed with " <> show exception
    putTextLn msg
    text msg

main :: IO ()
main = do
    -- Define the API routes handled by your web-application
    let routes = [ get "/api/a" (text "a\n")
                 , get "/api/b" (text "b\n")
                 , post "/api/capture/:id"
                   (do idVal :: Int <- getCapture "id"
                       text $ (T.pack (show idVal) `T.append` "\n")
                 , get "/api/isOdd/:val"
                   (do val :: Integer <- getCapture "val"
                       -- if val is odd return the number else we short-circuit the handler
                       unless (odd val) finish
                       text $ show val
                 , get "/api/showEnv" (do env <- getAppEnv
                                          text env
                 , get "/aaah" (liftIO $ E.throwString "oops!")

        -- Set the routes definition and exception handler for your
        -- web-application
        webbyConfig = setExceptionHandler (appExceptionHandler "MyApp") $
                      setRoutes routes $

        -- Application environment in this example is a simple Text literal.
        -- Usually, application environment would contain database connections
        -- etc.
        appEnv = "MyEnv" :: T.Text

    webbyApp <- mkWebbyApp appEnv webbyConfig
    putStrLn "Starting webserver..."
    W.runEnv 7000 webbyApp

You can try the example above, by cloning the repo and running the example:

$ examples/Basic.hs

In another shell, let’s curl the server:

$ curl http://localhost:7000/api/a
$ curl http://localhost:7000/api/b
$ curl -XPOST http://localhost:7000/api/capture/32
$ curl http://localhost:7000/api/showEnv
$ curl http://localhost:7000/aaah
MyApp failed with Control.Exception.Safe.throwString called with:

Called from:
  throwString (examples/Basic.hs:55:42 in main:Main)