generate API docs for your servant webservice

Version on this page:
LTS Haskell 19.14:0.12@rev:2
Stackage Nightly 2022-07-06:0.12@rev:2
Latest on Hackage:0.12@rev:2

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BSD-3-Clause licensed by Alp Mestanogullari, Sönke Hahn, Julian K. Arni
Maintained by
This version can be pinned in stack with:servant-docs-,1969

Module documentation for



Generate API docs for your servant webservice. Feel free to also take a look at servant-pandoc which uses this package to target a broad range of output formats using the excellent pandoc.


See here for the output of the following program.

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE OverloadedStrings #-}

import Data.Proxy
import Data.Text
import Servant

-- our type for a Greeting message
data Greet = Greet { _msg :: Text }
  deriving (Generic, Show)

-- we get our JSON serialization for free. This will be used by the default
-- 'MimeRender' instance for 'JSON'.
instance FromJSON Greet
instance ToJSON Greet

-- We can also implement 'MimeRender' explicitly for additional formats.
instance MimeRender PlainText Greet where
    mimeRender Proxy (Greet s) = "<h1>" <> cs s <> "</h1>"

-- we provide a sample value for the 'Greet' type
instance ToSample Greet where
  toSample = Just g

    where g = Greet "Hello, haskeller!"

instance ToParam (QueryParam "capital" Bool) where
  toParam _ =
    DocQueryParam "capital"
                  ["true", "false"]
                  "Get the greeting message in uppercase (true) or not (false). Default is false."

instance ToCapture (Capture "name" Text) where
  toCapture _ = DocCapture "name" "name of the person to greet"

instance ToCapture (Capture "greetid" Text) where
  toCapture _ = DocCapture "greetid" "identifier of the greet msg to remove"

-- API specification
type TestApi =
       "hello" :> Capture "name" Text :> QueryParam "capital" Bool :> Get '[JSON,PlainText] Greet
  :<|> "greet" :> RQBody '[JSON] Greet :> Post '[JSON] Greet
  :<|> "delete" :> Capture "greetid" Text :> Delete '[] ()

testApi :: Proxy TestApi
testApi = Proxy

-- Generate the Documentation's ADT
greetDocs :: API
greetDocs = docs testApi

main :: IO ()
main = putStrLn $ markdown greetDocs




  • Delete now is like Get, Post, Put, and Patch and returns a response body
  • Allow for extra information to be added to the docs
  • Support content-type aware combinators of servant-0.4
  • Render endpoints in a canonical order (
  • Remove ToJSON superclass from ToSample
  • Split out Internal module
  • Add support for response headers
  • Allow ToSample to return a different type than it’s arguments
  • Add Proxy argument to ToSample


  • Add the ability to display multiple responses, with some accompanying Text to describe the context in which we get the corresponding JSON.
  • Expose the headers lens
  • Represent an endpoint’s path as [String] (previously String), fixing a corner case where the leading / would be missing.