diff --git a/server/Makefile b/server/Makefile
index 9226084..e1cab5e 100644
--- a/server/Makefile
+++ b/server/Makefile
@@ -12,7 +12,7 @@ build:
 
 run:
 	$(MAKE) build
-	./knowyt
+	./knowyt -v
 
 run-loop:
 	pexec -R -c -e TARGET \
diff --git a/server/src/application/collectQuotes.go b/server/src/application/collectQuotes.go
index 73ce38d..8ff670c 100644
--- a/server/src/application/collectQuotes.go
+++ b/server/src/application/collectQuotes.go
@@ -3,6 +3,8 @@ package application
 import (
 	"fmt"
 	"net/http"
+
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/user"
 )
 
@@ -23,7 +25,7 @@ func (app *Application) CollectQuotes(usr *user.User, w http.ResponseWriter, r *
 
 	gm.CollectQuotes()
 	if err := app.saveGameState(gm); err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		w.WriteHeader(http.StatusInternalServerError)
 		fmt.Fprintf(w, "couldn't save game state")
 		return
diff --git a/server/src/application/continueGame.go b/server/src/application/continueGame.go
index 41672e1..95b4cf8 100644
--- a/server/src/application/continueGame.go
+++ b/server/src/application/continueGame.go
@@ -3,6 +3,8 @@ package application
 import (
 	"fmt"
 	"net/http"
+
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/user"
 )
 
@@ -24,6 +26,6 @@ func (app *Application) ContinueGame(usr *user.User, w http.ResponseWriter, r *h
 	gm.ContinueGame()
 
 	if err := app.saveGameState(gm); err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 	}
 }
diff --git a/server/src/application/createGame.go b/server/src/application/createGame.go
index 14a9099..6d40e69 100644
--- a/server/src/application/createGame.go
+++ b/server/src/application/createGame.go
@@ -3,15 +3,17 @@ package application
 import (
 	"encoding/json"
 	"fmt"
-	"github.com/google/uuid"
 	"math/rand"
 	"net/http"
 	"os"
 	"path"
-	"sirlab.de/go/knowyt/game"
-	"sirlab.de/go/knowyt/user"
 	"strconv"
 	"time"
+
+	"github.com/google/uuid"
+	"sirlab.de/go/knowyt/game"
+	"sirlab.de/go/knowyt/log"
+	"sirlab.de/go/knowyt/user"
 )
 
 type PlayerInfo struct {
@@ -36,7 +38,7 @@ func (app *Application) CreateGame(w http.ResponseWriter, r *http.Request) {
 	gm, err := app.createGame(teamname, lang)
 	if err != nil {
 		w.WriteHeader(http.StatusInternalServerError)
-		fmt.Printf("%v\n", err)
+		log.ErrorLog(err)
 		fmt.Fprintf(w, "server error")
 		return
 	}
@@ -44,7 +46,7 @@ func (app *Application) CreateGame(w http.ResponseWriter, r *http.Request) {
 	_, err = app.createUser(gm, name, user.ROLE_GAMEMASTER, authcode)
 	if err != nil {
 		w.WriteHeader(http.StatusInternalServerError)
-		fmt.Printf("%v\n", err)
+		log.ErrorLog(err)
 		fmt.Fprintf(w, "server error")
 		return
 	}
@@ -53,11 +55,11 @@ func (app *Application) CreateGame(w http.ResponseWriter, r *http.Request) {
 		Status:   "ok",
 		Authcode: authcode,
 	}
-	fmt.Printf("Name %s, Teamname %s, Authcode %s\n", name, teamname, authcode)
+	log.Debug("Name %s, Teamname %s, Authcode %s\n", name, teamname, authcode)
 
 	w.Header().Add("Content-Type", "application/json")
 	jsonString, _ := json.Marshal(playerInfo)
-	fmt.Fprintf(w, string(jsonString))
+	fmt.Fprintf(w, "%s", string(jsonString))
 }
 
 func (app *Application) createGame(gamename, lang string) (*game.Game, error) {
@@ -72,11 +74,12 @@ func (app *Application) createGame(gamename, lang string) (*game.Game, error) {
 	if err := os.Mkdir(quotesDirName, 0777); err != nil {
 		return nil, err
 	}
-	fmt.Printf("createGame(\"%s\": \"%s\" [%s])\n", gameId, gamename, lang)
+	log.Info("createGame(\"%s\": \"%s\" [%s])\n", gameId, gamename, lang)
 	gm, err := game.NewGame(gameId, gameFileName, gamename, lang)
 	if err != nil {
 		return nil, err
 	}
+
 	if err := gm.SaveGame(); err != nil {
 		return nil, err
 	}
diff --git a/server/src/application/deletePlayer.go b/server/src/application/deletePlayer.go
index 479580a..f42abb1 100644
--- a/server/src/application/deletePlayer.go
+++ b/server/src/application/deletePlayer.go
@@ -3,6 +3,8 @@ package application
 import (
 	"fmt"
 	"net/http"
+
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/user"
 )
 
@@ -25,20 +27,20 @@ func (app *Application) DeletePlayer(usr *user.User, w http.ResponseWriter, r *h
 	deleteUser := app.users[id]
 	if deleteUser.GetId() != id || deleteUser.GetGameId() != gm.GetId() {
 		w.WriteHeader(http.StatusForbidden)
-		fmt.Printf("couldn't find player %s in game %s\n", id, gm.GetId())
+		log.Warn("couldn't find player %s in game %s\n", id, gm.GetId())
 		fmt.Fprintf(w, "forbidden")
 		return
 	}
 	if deleteUser.GetId() == usr.GetId() {
 		w.WriteHeader(http.StatusForbidden)
-		fmt.Printf("can't delete yourself\n")
+		log.Warn("can't delete yourself\n")
 		fmt.Fprintf(w, "forbidden")
 		return
 	}
 
 	if err := deleteUser.DeleteUser(); err != nil {
 		w.WriteHeader(http.StatusInternalServerError)
-		fmt.Printf("%v\n", err)
+		log.ErrorLog(err)
 		fmt.Fprintf(w, "internal server error")
 		return
 	}
diff --git a/server/src/application/finishGame.go b/server/src/application/finishGame.go
index 69a8081..c92fd60 100644
--- a/server/src/application/finishGame.go
+++ b/server/src/application/finishGame.go
@@ -3,6 +3,8 @@ package application
 import (
 	"fmt"
 	"net/http"
+
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/user"
 )
 
@@ -22,7 +24,7 @@ func (app *Application) FinishGame(usr *user.User, w http.ResponseWriter, r *htt
 	}
 
 	if err := app.saveGameState(gm); err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		w.WriteHeader(http.StatusInternalServerError)
 		fmt.Fprintf(w, "couldn't save game state")
 		return
@@ -31,7 +33,7 @@ func (app *Application) FinishGame(usr *user.User, w http.ResponseWriter, r *htt
 	gm.FinishGame()
 
 	if err := app.saveGameState(gm); err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		w.WriteHeader(http.StatusInternalServerError)
 		fmt.Fprintf(w, "couldn't save game state")
 		return
diff --git a/server/src/application/getGameInfo.go b/server/src/application/getGameInfo.go
index 1dfee15..7e00a8d 100644
--- a/server/src/application/getGameInfo.go
+++ b/server/src/application/getGameInfo.go
@@ -4,6 +4,8 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/user"
 )
 
@@ -25,7 +27,7 @@ func (app *Application) GetGameInfo(usr *user.User, w http.ResponseWriter, r *ht
 	gameInfo := gm.GetGameInfo()
 	for i, _ := range gameInfo.Players {
 		if playerUser, err := app.GetUserById(gameInfo.Players[i].Id); err != nil {
-			fmt.Printf("GetUserById() failed: couldn't find player %s\n", gameInfo.Players[i].Id)
+			log.Warn("GetUserById() failed: couldn't find player %s\n", gameInfo.Players[i].Id)
 			w.WriteHeader(http.StatusInternalServerError)
 			fmt.Fprintf(w, "internal server error")
 			return
diff --git a/server/src/application/getGames.go b/server/src/application/getGames.go
index 0626bed..c2e4809 100644
--- a/server/src/application/getGames.go
+++ b/server/src/application/getGames.go
@@ -4,7 +4,9 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+
 	"sirlab.de/go/knowyt/game"
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/user"
 )
 
@@ -31,7 +33,7 @@ func (app *Application) GetGames(usr *user.User, w http.ResponseWriter, r *http.
 	for k, gameInfo := range games.Games {
 		for i, _ := range gameInfo.Players {
 			if playerUser, err := app.GetUserById(gameInfo.Players[i].Id); err != nil {
-				fmt.Printf("GetUserById() failed: couldn't find player %s\n", gameInfo.Players[i].Id)
+				log.Warn("GetUserById() failed: couldn't find player %s\n", gameInfo.Players[i].Id)
 				w.WriteHeader(http.StatusInternalServerError)
 				fmt.Fprintf(w, "internal server error")
 				return
diff --git a/server/src/application/getQuotes.go b/server/src/application/getQuotes.go
index aaa6267..fe2cc66 100644
--- a/server/src/application/getQuotes.go
+++ b/server/src/application/getQuotes.go
@@ -4,6 +4,8 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/user"
 )
 
@@ -11,15 +13,15 @@ func (app *Application) GetQuotes(usr *user.User, w http.ResponseWriter, r *http
 	gameRef := r.URL.Query().Get("g")
 	gm, err := app.GetGameById(gameRef)
 	if err != nil {
-		fmt.Printf("attempt to get quotes for invalid game id %s\n", gameRef)
+		log.Warn("attempt to get quotes for invalid game id %s\n", gameRef)
 		w.WriteHeader(http.StatusNotFound)
 		fmt.Fprintf(w, "game not found")
 		return
 	}
 
 	if usr.GetGameId() != gameRef && !usr.IsGamemaster() {
-		fmt.Printf("user's game id is %s\n", usr.GetGameId())
-		fmt.Printf("user not allowed to access game id %s\n", gameRef)
+		log.Warn("user's game id is %s\n", usr.GetGameId())
+		log.Warn("user not allowed to access game id %s\n", gameRef)
 		w.WriteHeader(http.StatusForbidden)
 		fmt.Fprintf(w, "forbidden")
 		return
diff --git a/server/src/application/removeQuote.go b/server/src/application/removeQuote.go
index 38bf326..ea9e395 100644
--- a/server/src/application/removeQuote.go
+++ b/server/src/application/removeQuote.go
@@ -4,6 +4,8 @@ import (
 	"fmt"
 	"net/http"
 	"path"
+
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/user"
 )
 
@@ -28,7 +30,7 @@ func (app *Application) RemoveQuote(usr *user.User, w http.ResponseWriter, r *ht
 	quoteFileName := path.Join(gameDirName, "quotes", quoteFileNameShort)
 
 	if err := gm.RemoveQuote(quoteFileName, usr.GetId(), quoteId); err != nil {
-		fmt.Printf("%s\n", err)
+		log.ErrorLog(err)
 		w.WriteHeader(http.StatusForbidden)
 		fmt.Fprintf(w, "forbidden")
 		return
diff --git a/server/src/application/resetGame.go b/server/src/application/resetGame.go
index a230a6a..017d83c 100644
--- a/server/src/application/resetGame.go
+++ b/server/src/application/resetGame.go
@@ -3,6 +3,8 @@ package application
 import (
 	"fmt"
 	"net/http"
+
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/user"
 )
 
@@ -24,7 +26,7 @@ func (app *Application) ResetGame(usr *user.User, w http.ResponseWriter, r *http
 	gm.ResetGame()
 
 	if err := app.saveGameState(gm); err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		w.WriteHeader(http.StatusInternalServerError)
 		fmt.Fprintf(w, "couldn't save game state")
 		return
diff --git a/server/src/application/savePlayer.go b/server/src/application/savePlayer.go
index 44ae679..1f4352b 100644
--- a/server/src/application/savePlayer.go
+++ b/server/src/application/savePlayer.go
@@ -3,9 +3,11 @@ package application
 import (
 	"fmt"
 	"net/http"
-	"sirlab.de/go/knowyt/game"
-	"sirlab.de/go/knowyt/user"
 	"strconv"
+
+	"sirlab.de/go/knowyt/game"
+	"sirlab.de/go/knowyt/log"
+	"sirlab.de/go/knowyt/user"
 )
 
 func (app *Application) SavePlayer(usr *user.User, w http.ResponseWriter, r *http.Request) {
@@ -29,14 +31,14 @@ func (app *Application) SavePlayer(usr *user.User, w http.ResponseWriter, r *htt
 	authcode := r.URL.Query().Get("authcode")
 	if name == "" {
 		w.WriteHeader(http.StatusBadRequest)
-		fmt.Printf("player name must not be empty\n")
+		log.Warn("player name must not be empty\n")
 		fmt.Fprintf(w, "server error")
 		return
 	}
 	if id != "" {
 		if err := app.modifyUser(id, gm, name, authcode); err != nil {
 			w.WriteHeader(http.StatusInternalServerError)
-			fmt.Printf("%v\n", err)
+			log.ErrorLog(err)
 			fmt.Fprintf(w, "server error")
 			return
 		}
@@ -44,7 +46,7 @@ func (app *Application) SavePlayer(usr *user.User, w http.ResponseWriter, r *htt
 		newPlayerId, err := app.createUser(gm, name, user.ROLE_PLAYER, authcode)
 		if err != nil {
 			w.WriteHeader(http.StatusInternalServerError)
-			fmt.Printf("%v\n", err)
+			log.ErrorLog(err)
 			fmt.Fprintf(w, "server error")
 			return
 		} else {
@@ -54,7 +56,7 @@ func (app *Application) SavePlayer(usr *user.User, w http.ResponseWriter, r *htt
 
 	if err := app.updateScore(gm, id, score); err != nil {
 		w.WriteHeader(http.StatusInternalServerError)
-		fmt.Printf("%v\n", err)
+		log.ErrorLog(err)
 		fmt.Fprintf(w, "server error")
 		return
 	}
diff --git a/server/src/application/saveQuote.go b/server/src/application/saveQuote.go
index ab3f49c..6ffba4f 100644
--- a/server/src/application/saveQuote.go
+++ b/server/src/application/saveQuote.go
@@ -7,6 +7,7 @@ import (
 
 	"github.com/google/uuid"
 	"sirlab.de/go/knowyt/game"
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/user"
 )
 
@@ -47,7 +48,7 @@ func (app *Application) SaveQuote(usr *user.User, w http.ResponseWriter, r *http
 	}
 
 	if err != nil {
-		fmt.Printf("%s", err)
+		log.ErrorLog(err)
 		w.WriteHeader(http.StatusForbidden)
 		fmt.Fprintf(w, "forbidden")
 		return
diff --git a/server/src/application/setGameLang.go b/server/src/application/setGameLang.go
index 43d6e6d..e18b9b8 100644
--- a/server/src/application/setGameLang.go
+++ b/server/src/application/setGameLang.go
@@ -3,6 +3,8 @@ package application
 import (
 	"fmt"
 	"net/http"
+
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/user"
 )
 
@@ -24,7 +26,7 @@ func (app *Application) SetGameLang(usr *user.User, w http.ResponseWriter, r *ht
 	lang := r.URL.Query().Get("lang")
 	if err := gm.SetGameLang(lang); err != nil {
 		w.WriteHeader(http.StatusInternalServerError)
-		fmt.Printf("%v", err)
+		log.ErrorLog(err)
 		fmt.Fprintf(w, "server error")
 		return
 	}
diff --git a/server/src/application/setGameName.go b/server/src/application/setGameName.go
index 281754a..d591b54 100644
--- a/server/src/application/setGameName.go
+++ b/server/src/application/setGameName.go
@@ -3,6 +3,8 @@ package application
 import (
 	"fmt"
 	"net/http"
+
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/user"
 )
 
@@ -24,7 +26,7 @@ func (app *Application) SetGameName(usr *user.User, w http.ResponseWriter, r *ht
 	name := r.URL.Query().Get("name")
 	if err := gm.SetGameName(name); err != nil {
 		w.WriteHeader(http.StatusInternalServerError)
-		fmt.Printf("%v", err)
+		log.ErrorLog(err)
 		fmt.Fprintf(w, "server error")
 		return
 	}
diff --git a/server/src/application/startGame.go b/server/src/application/startGame.go
index 67180d6..f96e931 100644
--- a/server/src/application/startGame.go
+++ b/server/src/application/startGame.go
@@ -3,6 +3,8 @@ package application
 import (
 	"fmt"
 	"net/http"
+
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/user"
 )
 
@@ -24,7 +26,7 @@ func (app *Application) StartGame(usr *user.User, w http.ResponseWriter, r *http
 	gm.StartGame()
 
 	if err := app.saveGameState(gm); err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		w.WriteHeader(http.StatusInternalServerError)
 		fmt.Fprintf(w, "couldn't save game state")
 		return
diff --git a/server/src/applicationConfig/appconfig.go b/server/src/applicationConfig/appconfig.go
index 3de92b5..25e7d3c 100644
--- a/server/src/applicationConfig/appconfig.go
+++ b/server/src/applicationConfig/appconfig.go
@@ -1,10 +1,30 @@
 package applicationConfig
 
+import (
+	"flag"
+
+	"sirlab.de/go/knowyt/log"
+)
+
 type ApplicationConfig struct {
 	DataDir string
 }
 
 func NewApplicationConfig() ApplicationConfig {
+
+	flagVerbose := flag.Bool("v", false, "log debug messages, too")
+	flagQuiet := flag.Bool("q", false, "be quiet; warning and error messages only")
+	flag.Parse()
+
+	log.SetLoglevel(log.LOG_INFO)
+
+	if *flagVerbose {
+		log.SetLoglevel(log.LOG_DEBUG)
+	}
+	if *flagQuiet {
+		log.SetLoglevel(log.LOG_WARN)
+	}
+
 	return ApplicationConfig{
 		DataDir: "data/",
 	}
diff --git a/server/src/engine/publish.go b/server/src/engine/publish.go
index 6d14179..0510e60 100644
--- a/server/src/engine/publish.go
+++ b/server/src/engine/publish.go
@@ -1,7 +1,7 @@
 package engine
 
 import (
-	"fmt"
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/syncdata"
 )
 
@@ -18,6 +18,6 @@ func (eng *Engine) publish(populateSyncDataCb PopulateSyncDataCb) {
 		populateSyncDataCb(&data)
 	}
 
-	fmt.Printf("%s engine versionRef %d\n", data.GameInfo.GameId, eng.versionRef)
+	log.Debug("%s engine versionRef %d\n", data.GameInfo.GameId, eng.versionRef)
 	eng.obs.Update(data)
 }
diff --git a/server/src/engine/sync.go b/server/src/engine/sync.go
index 84bc12c..065c607 100644
--- a/server/src/engine/sync.go
+++ b/server/src/engine/sync.go
@@ -4,8 +4,9 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
-	"sirlab.de/go/knowyt/syncdata"
 	"strconv"
+
+	"sirlab.de/go/knowyt/syncdata"
 )
 
 func (eng *Engine) SyncHandler(w http.ResponseWriter, r *http.Request) {
@@ -25,13 +26,11 @@ func (eng *Engine) SyncHandler(w http.ResponseWriter, r *http.Request) {
 			break
 		}
 
-		select {
-		case <-stream.Changes():
-			stream.Next()
-		}
+		<-stream.Changes()
+		stream.Next()
 	}
 
 	jsonString, _ := json.MarshalIndent(value, "", "  ")
 	w.Header().Add("Content-Type", "application/json")
-	fmt.Fprintf(w, string(jsonString))
+	fmt.Fprintf(w, "%s", string(jsonString))
 }
diff --git a/server/src/game/collectQuotes.go b/server/src/game/collectQuotes.go
index 3ea2ca9..9a6fdf8 100644
--- a/server/src/game/collectQuotes.go
+++ b/server/src/game/collectQuotes.go
@@ -1,13 +1,13 @@
 package game
 
 import (
-	"fmt"
+	"sirlab.de/go/knowyt/log"
 )
 
 func (gm *Game) CollectQuotes() {
 	err := gm.changeGameState(STATE_IDLE, STATE_COLLECT, PHASE_NONE)
 	if err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		return
 	}
 
diff --git a/server/src/game/continueGame.go b/server/src/game/continueGame.go
index 860533d..c05677e 100644
--- a/server/src/game/continueGame.go
+++ b/server/src/game/continueGame.go
@@ -1,13 +1,13 @@
 package game
 
 import (
-	"fmt"
+	"sirlab.de/go/knowyt/log"
 )
 
 func (gm *Game) ContinueGame() {
 	state, phase := gm.GetState()
 	if state != STATE_PLAY {
-		fmt.Printf("invalid state, can't continue game in %s state\n", state)
+		log.Warn("invalid state, can't continue game in %s state\n", state)
 		return
 	}
 
@@ -19,7 +19,7 @@ func (gm *Game) ContinueGame() {
 	case PHASE_REVEAL_SOURCE:
 		gm.nextRound()
 	default:
-		fmt.Printf("invalid state, can't continue game in %s state, %s phase\n", state, phase)
+		log.Warn("invalid state, can't continue game in %s state, %s phase\n", state, phase)
 		return
 	}
 }
diff --git a/server/src/game/finishGame.go b/server/src/game/finishGame.go
index 49b0409..57ab23e 100644
--- a/server/src/game/finishGame.go
+++ b/server/src/game/finishGame.go
@@ -1,13 +1,13 @@
 package game
 
 import (
-	"fmt"
+	"sirlab.de/go/knowyt/log"
 )
 
 func (gm *Game) FinishGame() {
 	state, _ := gm.GetState()
 	if state != STATE_IDLE && state != STATE_PLAY {
-		fmt.Printf("%s invalid state, can't finish game in %s state\n", gm.id, state)
+		log.Warn("%s invalid state, can't finish game in %s state\n", gm.id, state)
 		return
 	}
 
diff --git a/server/src/game/nextRound.go b/server/src/game/nextRound.go
index a0997c1..c213d59 100644
--- a/server/src/game/nextRound.go
+++ b/server/src/game/nextRound.go
@@ -1,13 +1,14 @@
 package game
 
 import (
-	"fmt"
 	"time"
+
+	"sirlab.de/go/knowyt/log"
 )
 
 func (gm *Game) nextRound() {
 	if err := gm.changeGamePhase(STATE_PLAY, PHASE_REVEAL_SOURCE, PHASE_ROUND_END); err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		return
 	}
 	gm.notifyClients()
@@ -16,7 +17,7 @@ func (gm *Game) nextRound() {
 
 	err := gm.changeGameState(STATE_PLAY, STATE_READY_SET, "Go!")
 	if err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		return
 	}
 	gm.notifyClients()
@@ -25,7 +26,7 @@ func (gm *Game) nextRound() {
 
 	err = gm.changeGameState(STATE_READY_SET, STATE_READY_SET, "")
 	if err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		return
 	}
 	gm.notifyClients()
@@ -34,7 +35,7 @@ func (gm *Game) nextRound() {
 
 	err = gm.changeGameState(STATE_READY_SET, STATE_PLAY, PHASE_NONE)
 	if err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		return
 	}
 	gm.runRound()
diff --git a/server/src/game/player.go b/server/src/game/player.go
index 1330c87..7d1e1c5 100644
--- a/server/src/game/player.go
+++ b/server/src/game/player.go
@@ -1,7 +1,7 @@
 package game
 
 import (
-	"fmt"
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/user"
 )
 
@@ -24,9 +24,9 @@ func (gm *Game) EventPlayerJoins(usr *user.User) {
 	gm.players[usrId] = player
 
 	if prevPlayer.id != "" {
-		fmt.Printf("%s player \"%s\" re-joined\n", gm.id, gm.players[usrId].name)
+		log.Debug("%s player \"%s\" re-joined\n", gm.id, gm.players[usrId].name)
 	} else {
-		fmt.Printf("%s player \"%s\" joined\n", gm.id, usrName)
+		log.Debug("%s player \"%s\" joined\n", gm.id, usrName)
 	}
 
 	gm.eng.Update()
@@ -45,7 +45,7 @@ func (gm *Game) EventPlayerLeaves(usr *user.User) {
 	player.isIdle = true
 	gm.players[usrId] = player
 
-	fmt.Printf("%s player \"%s\" is idle\n", gm.id, usr.GetName())
+	log.Debug("%s player \"%s\" is idle\n", gm.id, usr.GetName())
 
 	gm.eng.Update()
 }
diff --git a/server/src/game/populateGetRoundInfo.go b/server/src/game/populateGetRoundInfo.go
index 78249f8..dc435f9 100644
--- a/server/src/game/populateGetRoundInfo.go
+++ b/server/src/game/populateGetRoundInfo.go
@@ -1,7 +1,7 @@
 package game
 
 import (
-	"fmt"
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/syncdata"
 )
 
@@ -12,7 +12,7 @@ func (gm *Game) populateGetRoundInfo() *syncdata.RoundInfo {
 
 	quote := gm.quotes[gm.round.quoteId]
 	if quote == nil {
-		fmt.Printf("%s fatal error: quote id \"%s\" not found\n", gm.id, gm.round.quoteId)
+		log.Error("%s fatal error: quote id \"%s\" not found\n", gm.id, gm.round.quoteId)
 		return nil
 	}
 
diff --git a/server/src/game/revealShowCount.go b/server/src/game/revealShowCount.go
index 06157b4..3e26636 100644
--- a/server/src/game/revealShowCount.go
+++ b/server/src/game/revealShowCount.go
@@ -1,17 +1,17 @@
 package game
 
 import (
-	"fmt"
+	"sirlab.de/go/knowyt/log"
 )
 
 func (gm *Game) revealShowCount() {
 	if !gm.allPlayersHaveSelectedAQuote() {
-		fmt.Printf("%s not all players have selected a quote yet\n", gm.GetId())
+		log.Warn("%s not all players have selected a quote yet\n", gm.GetId())
 		return
 	}
 
 	if err := gm.changeGamePhase(STATE_PLAY, PHASE_SELECT_QUOTE, PHASE_REVEAL_SHOW_COUNT); err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		return
 	}
 	for key, val := range gm.round.selections {
diff --git a/server/src/game/revealSource.go b/server/src/game/revealSource.go
index a93dd91..68d016a 100644
--- a/server/src/game/revealSource.go
+++ b/server/src/game/revealSource.go
@@ -1,12 +1,12 @@
 package game
 
 import (
-	"fmt"
+	"sirlab.de/go/knowyt/log"
 )
 
 func (gm *Game) revealSource() {
 	if err := gm.changeGamePhase(STATE_PLAY, PHASE_REVEAL_SHOW_COUNT, PHASE_REVEAL_SOURCE); err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		return
 	}
 
diff --git a/server/src/game/runCountdown.go b/server/src/game/runCountdown.go
index 0857ca2..b85b1b2 100644
--- a/server/src/game/runCountdown.go
+++ b/server/src/game/runCountdown.go
@@ -1,8 +1,9 @@
 package game
 
 import (
-	"fmt"
 	"time"
+
+	"sirlab.de/go/knowyt/log"
 )
 
 func (gm *Game) runCountdown() {
@@ -17,7 +18,7 @@ func (gm *Game) runCountdown() {
 
 	err := gm.changeGameState(STATE_IDLE, STATE_READY_SET, phases[0])
 	if err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		return
 	}
 	gm.notifyClients()
@@ -26,7 +27,7 @@ func (gm *Game) runCountdown() {
 	for i := 1; i < len(phases); i++ {
 		err = gm.changeGamePhase(STATE_READY_SET, phases[i-1], phases[i])
 		if err != nil {
-			fmt.Println(err)
+			log.ErrorLog(err)
 			return
 		}
 		gm.notifyClients()
@@ -35,7 +36,7 @@ func (gm *Game) runCountdown() {
 
 	err = gm.changeGameState(STATE_READY_SET, STATE_PLAY, PHASE_NONE)
 	if err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		return
 	}
 
diff --git a/server/src/game/runFinal.go b/server/src/game/runFinal.go
index 33869cc..c0f285a 100644
--- a/server/src/game/runFinal.go
+++ b/server/src/game/runFinal.go
@@ -1,19 +1,19 @@
 package game
 
 import (
-	"fmt"
+	"sirlab.de/go/knowyt/log"
 )
 
 func (gm *Game) runFinal() {
 	state, _ := gm.GetState()
 	if state != STATE_IDLE && state != STATE_PLAY {
-		fmt.Printf("%s expected state \"IDLE\" | \"PLAY\" != \"%s\"", gm.GetId(), state)
+		log.Warn("%s expected state \"IDLE\" | \"PLAY\" != \"%s\"", gm.GetId(), state)
 		return
 	}
 
 	err := gm.changeGameState(STATE_ANY, STATE_FINAL, PHASE_NONE)
 	if err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		return
 	}
 
diff --git a/server/src/game/runRound.go b/server/src/game/runRound.go
index 0d37055..c5785dc 100644
--- a/server/src/game/runRound.go
+++ b/server/src/game/runRound.go
@@ -1,19 +1,19 @@
 package game
 
 import (
-	"fmt"
+	"sirlab.de/go/knowyt/log"
 )
 
 func (gm *Game) runRound() {
 	state, _ := gm.GetState()
 	if state != STATE_IDLE && state != STATE_PLAY && state != STATE_COLLECT {
-		fmt.Printf("%s expected state \"IDLE\" | \"PLAY\" | \"COLLECT\" != \"%s\"", gm.GetId(), state)
+		log.Warn("%s expected state \"IDLE\" | \"PLAY\" | \"COLLECT\" != \"%s\"", gm.GetId(), state)
 		return
 	}
 
 	err := gm.changeGameState(STATE_ANY, STATE_PLAY, PHASE_SELECT_QUOTE)
 	if err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		return
 	}
 
diff --git a/server/src/game/saveSelection.go b/server/src/game/saveSelection.go
index 5bc9f12..5264421 100644
--- a/server/src/game/saveSelection.go
+++ b/server/src/game/saveSelection.go
@@ -1,7 +1,7 @@
 package game
 
 import (
-	"fmt"
+	"sirlab.de/go/knowyt/log"
 	"sirlab.de/go/knowyt/user"
 )
 
@@ -26,5 +26,5 @@ func (gm *Game) updateSelection(usr *user.User, selection string) {
 		}
 	}
 
-	fmt.Printf("%s invalid selection id \"%s\"\n", gm.id, selection)
+	log.Warn("%s invalid selection id \"%s\"\n", gm.id, selection)
 }
diff --git a/server/src/game/setupRound.go b/server/src/game/setupRound.go
index 0304c34..f1bdee3 100644
--- a/server/src/game/setupRound.go
+++ b/server/src/game/setupRound.go
@@ -3,8 +3,10 @@ package game
 import (
 	"fmt"
 	"math/rand"
-	"sirlab.de/go/knowyt/quote"
 	"time"
+
+	"sirlab.de/go/knowyt/log"
+	"sirlab.de/go/knowyt/quote"
 )
 
 func (gm *Game) setupRound() error {
@@ -66,7 +68,7 @@ func (gm *Game) selectQuote() error {
 func (gm *Game) getSourceById(id string) Source {
 	plInfo, err := gm.getPlayerById(id)
 	if err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		return Source{}
 	}
 
diff --git a/server/src/game/startGame.go b/server/src/game/startGame.go
index 18f0d99..5a709f6 100644
--- a/server/src/game/startGame.go
+++ b/server/src/game/startGame.go
@@ -1,7 +1,7 @@
 package game
 
 import (
-	"fmt"
+	"sirlab.de/go/knowyt/log"
 )
 
 func (gm *Game) StartGame() {
@@ -11,7 +11,7 @@ func (gm *Game) StartGame() {
 func (gm *Game) ResetGame() {
 	err := gm.changeGameState(STATE_ANY, STATE_IDLE, PHASE_NONE)
 	if err != nil {
-		fmt.Println(err)
+		log.ErrorLog(err)
 		return
 	}
 
diff --git a/server/src/go.mod b/server/src/go.mod
index 2120fde..eb916d3 100644
--- a/server/src/go.mod
+++ b/server/src/go.mod
@@ -1,6 +1,6 @@
 module sirlab.de/go/knowyt
 
-go 1.16
+go 1.18
 
 require (
 	github.com/google/uuid v1.3.0
diff --git a/server/src/handler/filehandler.go b/server/src/handler/filehandler.go
index 45b5c0a..6ed3eed 100644
--- a/server/src/handler/filehandler.go
+++ b/server/src/handler/filehandler.go
@@ -5,7 +5,9 @@ import (
 	"mime"
 	"net/http"
 	"path"
-	"sirlab.de/go/knowyt/resources"
+
+	"sirlab.de/go/knowyt/log"
+	Resources "sirlab.de/go/knowyt/resources"
 )
 
 func FileHandler(w http.ResponseWriter, req *http.Request) {
@@ -24,7 +26,7 @@ func FileHandler(w http.ResponseWriter, req *http.Request) {
 		}
 	}
 	if err != nil {
-		fmt.Printf("%s: %v\n", uri, err)
+		log.Error("%s: %v\n", uri, err)
 		http.NotFoundHandler().ServeHTTP(w, req)
 		return
 	}
diff --git a/server/src/knowyt.go b/server/src/knowyt.go
index 5b40436..765c2c8 100644
--- a/server/src/knowyt.go
+++ b/server/src/knowyt.go
@@ -1,18 +1,19 @@
 package main
 
 import (
-	"fmt"
 	"os"
+
 	"sirlab.de/go/knowyt/application"
 	"sirlab.de/go/knowyt/applicationConfig"
 	"sirlab.de/go/knowyt/handler"
+	"sirlab.de/go/knowyt/log"
 )
 
 func main() {
 	appConfig := applicationConfig.NewApplicationConfig()
 	app, err := application.NewApplication(appConfig)
 	if err != nil {
-		fmt.Printf("%v\n", err)
+		log.ErrorLog(err)
 		os.Exit(1)
 	}
 	mux := handler.NewAuthMux(app)
@@ -44,6 +45,6 @@ func main() {
 	mux.PublicHandleFunc("/", handler.FileHandler)
 
 	// start listening
-	fmt.Printf("http://localhost:%d/\n", mux.Port)
+	log.Info("http://localhost:%d/\n", mux.Port)
 	mux.ListenAndServe()
 }
diff --git a/server/src/log/main.go b/server/src/log/main.go
new file mode 100644
index 0000000..1a832b1
--- /dev/null
+++ b/server/src/log/main.go
@@ -0,0 +1,59 @@
+package log
+
+import (
+	"fmt"
+	"sync"
+)
+
+var lock = &sync.Mutex{}
+var loglevel = LOG_NONE
+
+func SetLoglevel(_loglevel int) {
+	lock.Lock()
+	defer lock.Unlock()
+
+	loglevel = _loglevel
+}
+
+func Debug(format string, v ...any) {
+	lock.Lock()
+	defer lock.Unlock()
+
+	if loglevel >= LOG_DEBUG {
+		fmt.Printf(format, v...)
+	}
+}
+
+func Info(format string, v ...any) {
+	lock.Lock()
+	defer lock.Unlock()
+
+	if loglevel >= LOG_INFO {
+		fmt.Printf(format, v...)
+	}
+}
+
+func Warn(format string, v ...any) {
+	lock.Lock()
+	defer lock.Unlock()
+
+	if loglevel >= LOG_WARN {
+		fmt.Printf(format, v...)
+	}
+}
+
+func Error(format string, v ...any) {
+	lock.Lock()
+	defer lock.Unlock()
+
+	if loglevel >= LOG_ERROR {
+		fmt.Printf(format, v...)
+	}
+}
+
+func ErrorLog(err error) {
+	lock.Lock()
+	defer lock.Unlock()
+
+	Error("%v\n", err)
+}
diff --git a/server/src/log/struct.go b/server/src/log/struct.go
new file mode 100644
index 0000000..24c9d2c
--- /dev/null
+++ b/server/src/log/struct.go
@@ -0,0 +1,13 @@
+package log
+
+const (
+	LOG_NONE = 1 << iota
+	LOG_ERROR
+	LOG_WARN
+	LOG_INFO
+	LOG_DEBUG
+)
+
+type Log struct {
+	Loglevel int
+}