diff --git a/app/main.go b/app/main.go
index 5792a95..a96090f 100644
--- a/app/main.go
+++ b/app/main.go
@@ -6,6 +6,8 @@ import (
 	"fmt"
 	"os"
 	"regexp"
+
+	"framagit.org/ppom/reaction/logger"
 )
 
 func addStringFlag(names []string, defvalue string, f *flag.FlagSet) *string {
@@ -42,6 +44,10 @@ func addLimitFlag(f *flag.FlagSet) *string {
 	return addStringFlag([]string{"l", "limit"}, "", f)
 }
 
+func addLevelFlag(f *flag.FlagSet) *string {
+	return addStringFlag([]string{"l", "loglevel"}, "INFO", f)
+}
+
 func subCommandParse(f *flag.FlagSet, maxRemainingArgs int) {
 	help := addBoolFlag([]string{"h", "help"}, f)
 	f.Parse(os.Args[2:])
@@ -70,6 +76,8 @@ func basicUsage() {
 
   # options:
     -c/--config CONFIG_FILE          # configuration file in json, jsonnet or yaml format (required)
+    -l/--loglevel LEVEL              # minimum log level to show, in DEBUG, INFO, WARN, ERROR, FATAL
+                                     # (default: INFO)
     -s/--socket SOCKET               # path to the client-daemon communication socket
                                      # (default: /run/reaction/reaction.sock)
 
@@ -102,7 +110,7 @@ var exampleConf string
 
 func Main() {
 	if len(os.Args) <= 1 {
-		fmt.Println("No argument provided")
+		logger.Fatalln("No argument provided")
 		basicUsage()
 		os.Exit(1)
 	} else if os.Args[1] == "-h" || os.Args[1] == "--help" {
@@ -121,12 +129,20 @@ func Main() {
 	case "start":
 		SocketPath = addSocketFlag(f)
 		confFilename := addConfFlag(f)
+		logLevel := addLevelFlag(f)
 		subCommandParse(f, 0)
 		if *confFilename == "" {
-			fmt.Println("no configuration file provided")
+			logger.Fatalln("no configuration file provided")
 			basicUsage()
 			os.Exit(1)
 		}
+		logLevelType := logger.FromString(*logLevel)
+		if logLevelType == logger.UNKNOWN {
+			logger.Fatalf("Log Level %v not recognized", logLevel)
+			basicUsage()
+			os.Exit(1)
+		}
+		logger.SetLogLevel(logLevelType)
 		Daemon(*confFilename)
 
 	case "show":
@@ -135,12 +151,12 @@ func Main() {
 		limit := addLimitFlag(f)
 		subCommandParse(f, 0)
 		if *queryFormat != "yaml" && *queryFormat != "json" {
-			fmt.Println("only yaml and json formats are supported")
+			logger.Fatalln("only yaml and json formats are supported")
 			f.PrintDefaults()
 			os.Exit(1)
 		}
 		if *limit != "" {
-			fmt.Println("for now, -l/--limit is not supported")
+			logger.Fatalln("for now, -l/--limit is not supported")
 			os.Exit(1)
 		}
 		// f.Arg(0) is "" if there is no remaining argument
@@ -152,17 +168,17 @@ func Main() {
 		limit := addLimitFlag(f)
 		subCommandParse(f, 1)
 		if *queryFormat != "yaml" && *queryFormat != "json" {
-			fmt.Println("only yaml and json formats are supported")
+			logger.Fatalln("only yaml and json formats are supported")
 			f.PrintDefaults()
 			os.Exit(1)
 		}
 		if f.Arg(0) == "" {
-			fmt.Println("subcommand flush takes one TARGET argument")
+			logger.Fatalln("subcommand flush takes one TARGET argument")
 			basicUsage()
 			os.Exit(1)
 		}
 		if *limit != "" {
-			fmt.Println("for now, -l/--limit is not supported")
+			logger.Fatalln("for now, -l/--limit is not supported")
 			os.Exit(1)
 		}
 		ClientFlush(f.Arg(0), *limit, *queryFormat)
@@ -171,17 +187,17 @@ func Main() {
 		// socket not needed, no interaction with the daemon
 		subCommandParse(f, 2)
 		if f.Arg(0) == "" {
-			fmt.Println("subcommand test-regex takes at least one REGEX argument")
+			logger.Fatalln("subcommand test-regex takes at least one REGEX argument")
 			basicUsage()
 			os.Exit(1)
 		}
 		regex, err := regexp.Compile(f.Arg(0))
 		if err != nil {
-			fmt.Printf("ERROR the specified regex is invalid: %v", err)
+			logger.Fatalln("ERROR the specified regex is invalid: %v", err)
 			os.Exit(1)
 		}
 		if f.Arg(1) == "" {
-			fmt.Println("INFO  no second argument: reading from stdin")
+			logger.Println(logger.INFO, "no second argument: reading from stdin")
 
 			MatchStdin(regex)
 		} else {
@@ -189,7 +205,7 @@ func Main() {
 		}
 
 	default:
-		fmt.Println("subcommand not recognized")
+		logger.Fatalln("subcommand not recognized")
 		basicUsage()
 		os.Exit(1)
 	}
diff --git a/logger/log.go b/logger/log.go
index 02ef71a..3f1eaeb 100644
--- a/logger/log.go
+++ b/logger/log.go
@@ -5,11 +5,12 @@ import "log"
 type Level int
 
 const (
-	DEBUG = Level(1)
-	INFO  = Level(2)
-	WARN  = Level(3)
-	ERROR = Level(4)
-	FATAL = Level(5)
+	UNKNOWN = Level(-1)
+	DEBUG   = Level(1)
+	INFO    = Level(2)
+	WARN    = Level(3)
+	ERROR   = Level(4)
+	FATAL   = Level(5)
 )
 
 func (l Level) String() string {
@@ -29,6 +30,23 @@ func (l Level) String() string {
 	}
 }
 
+func FromString(s string) Level {
+	switch s {
+	case "DEBUG":
+		return DEBUG
+	case "INFO":
+		return INFO
+	case "WARN":
+		return WARN
+	case "ERROR":
+		return ERROR
+	case "FATAL":
+		return FATAL
+	default:
+		return UNKNOWN
+	}
+}
+
 var LogLevel Level = 2
 
 func SetLogLevel(level Level) {
@@ -37,13 +55,16 @@ func SetLogLevel(level Level) {
 
 func Println(level Level, args ...any) {
 	if level >= LogLevel {
-		log.Println(level, args)
+		newargs := make([]any, 0)
+		newargs = append(newargs, level)
+		newargs = append(newargs, args...)
+		log.Println(newargs...)
 	}
 }
 
 func Printf(level Level, format string, args ...any) {
 	if level >= LogLevel {
-		log.Printf(level.String()+format, args)
+		log.Printf(level.String()+format, args...)
 	}
 }