diff --git a/package.yaml b/package.yaml
index bd296b3..ba2f5a2 100644
--- a/package.yaml
+++ b/package.yaml
@@ -23,6 +23,8 @@ dependencies:
 - base
 - lifted-base
 - aeson
+- aeson-pretty
+- bytestring
 - hashable
 - http-api-data
 - http-client
diff --git a/src/Telegram/Bot/Simple/Debug.hs b/src/Telegram/Bot/Simple/Debug.hs
new file mode 100644
index 0000000..46aca5b
--- /dev/null
+++ b/src/Telegram/Bot/Simple/Debug.hs
@@ -0,0 +1,87 @@
+module Telegram.Bot.Simple.Debug where
+
+import           Control.Monad.Trans        (liftIO)
+import           Control.Monad.Writer       (tell)
+import           Data.Aeson                 (ToJSON)
+import qualified Data.Aeson.Encode.Pretty   as Aeson
+import qualified Data.ByteString.Lazy.Char8 as BSL8
+import           Data.Monoid                ((<>))
+import           Debug.Trace                (trace)
+import qualified Telegram.Bot.API           as Telegram
+import           Telegram.Bot.Simple
+
+-- * Trace 'Telegram.Update's
+
+-- | Trace (debug print) every 'Telegram.Update' before parsing it.
+traceTelegramUpdatesWith
+  :: (Telegram.Update -> String)    -- ^ How to display an update.
+  -> BotApp model action
+  -> BotApp model action
+traceTelegramUpdatesWith f botApp = botApp
+  { botAction = \update -> botAction botApp (trace (f update) update)
+  }
+
+-- | Trace (debug print) every update as pretty JSON value.
+traceTelegramUpdatesJSON :: BotApp model action -> BotApp model action
+traceTelegramUpdatesJSON = traceTelegramUpdatesWith prettyJSONString
+
+-- | Trace (debug print) every update using 'Show' instance.
+traceTelegramUpdatesShow :: BotApp model action -> BotApp model action
+traceTelegramUpdatesShow = traceTelegramUpdatesWith show
+
+-- * Trace bot actions
+
+-- | Trace (debug print) every incoming and issued action.
+traceBotActionsWith
+  :: (action -> String)     -- ^ How to display an action.
+  -> BotApp model action
+  -> BotApp model action
+traceBotActionsWith f botApp = botApp { botHandler = newBotHandler }
+  where
+    traceAction action = action <$ do
+      liftIO $ putStrLn ("Issued action: " <> f action)
+
+    newBotHandler action model = do
+      Eff (tell (map (>>= traceAction) actions))
+      pure newModel
+      where
+        (newModel, actions) = runEff $
+          botHandler botApp
+            (trace ("Incoming action: " <> f action) action)
+            model
+
+-- | Trace (debug print) bot actions using 'Show' instance.
+traceBotActionsShow
+  :: Show action => BotApp model action -> BotApp model action
+traceBotActionsShow = traceBotActionsWith show
+
+-- * Trace bot state model
+
+-- | Trace (debug print) bot model.
+traceBotModelWith
+  :: (model -> String)    -- ^ How to display a model.
+  -> BotApp model action
+  -> BotApp model action
+traceBotModelWith f botApp = botApp
+  { botInitialModel = traceModel (botInitialModel botApp)
+  , botHandler = newHandler
+  }
+    where
+      traceModel = trace <$> f <*> id
+
+      newHandler action model = traceModel <$> botHandler botApp action model
+
+-- | Trace (debug print) bot model using 'Show' instance.
+traceBotModelShow
+  :: Show model => BotApp model action -> BotApp model action
+traceBotModelShow = traceBotModelWith show
+
+-- | Trace (debug print) bot model using 'Show' instance.
+traceBotModelJSON
+  :: ToJSON model => BotApp model action -> BotApp model action
+traceBotModelJSON = traceBotModelWith prettyJSONString
+
+-- * Helpers
+
+prettyJSONString :: ToJSON a => a -> String
+prettyJSONString = BSL8.unpack . Aeson.encodePretty