diff --git a/examples/client-example/main.go b/examples/client-example/main.go
index 5b38187..2c399ed 100644
--- a/examples/client-example/main.go
+++ b/examples/client-example/main.go
@@ -2,10 +2,10 @@ package main
 
 import (
 	"fmt"
+	"github.com/afiskon/promtail-client/promtail"
 	"log"
 	"os"
 	"time"
-	"github.com/afiskon/promtail-client/promtail"
 )
 
 func displayUsage() {
@@ -20,13 +20,13 @@ func displayInvalidName(arg string) {
 
 func nameIsValid(name string) bool {
 	for _, c := range name {
-        if !((c >= 'a' && c <= 'z') ||
-             (c >= 'A' && c <= 'Z') ||
-             (c >= '0' && c <= '9') ||
-             (c == '-') || (c == '_')) {
-            return false
-        }
-    }
+		if !((c >= 'a' && c <= 'z') ||
+			(c >= 'A' && c <= 'Z') ||
+			(c >= '0' && c <= '9') ||
+			(c == '-') || (c == '_')) {
+			return false
+		}
+	}
 	return true
 }
 
@@ -50,19 +50,19 @@ func main() {
 		displayInvalidName("job-name")
 	}
 
-	labels := "{source=\""+source_name+"\",job=\""+job_name+"\"}"
+	labels := "{source=\"" + source_name + "\",job=\"" + job_name + "\"}"
 	conf := promtail.ClientConfig{
 		PushURL:            "http://localhost:3100/api/prom/push",
 		Labels:             labels,
 		BatchWait:          5 * time.Second,
 		BatchEntriesNumber: 10000,
-		SendLevel: 			promtail.INFO,
-		PrintLevel: 		promtail.ERROR,
+		SendLevel:          promtail.INFO,
+		PrintLevel:         promtail.ERROR,
 	}
 
 	var (
 		loki promtail.Client
-		err error
+		err  error
 	)
 
 	if format == "proto" {
@@ -78,8 +78,8 @@ func main() {
 
 	for i := 1; i < 5; i++ {
 		tstamp := time.Now().String()
-		loki.Debugf("source = %s time = %s, i = %d\n", source_name, tstamp, i)
-		loki.Infof("source = %s, time = %s, i = %d\n", source_name, tstamp, i)
+		loki.Debugf("source=%s time = %s, i = %d\n", source_name, tstamp, i)
+		loki.Infof("source=%s, time = %s, i = %d\n", source_name, tstamp, i)
 		loki.Warnf("source = %s, time = %s, i = %d\n", source_name, tstamp, i)
 		loki.Errorf("source = %s, time = %s, i = %d\n", source_name, tstamp, i)
 		time.Sleep(1 * time.Second)
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..d9568f1
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,10 @@
+module github.com/afiskon/promtail-client
+
+go 1.17
+
+require (
+	github.com/golang/protobuf v1.5.2
+	github.com/golang/snappy v0.0.4
+)
+
+require google.golang.org/protobuf v1.26.0 // indirect
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..d0ca355
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,12 @@
+github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
+github.com/golang/protobuf v1.5.2 h1:ROPKBNFfQgOUMifHyP+KYbvpjbdoFNs+aK7DXlji0Tw=
+github.com/golang/protobuf v1.5.2/go.mod h1:XVQd3VNwM+JqD3oG2Ue2ip4fOMUkwXdXDdiuN0vRsmY=
+github.com/golang/snappy v0.0.4 h1:yAGX7huGHXlcLOEtBnF4w7FQwA26wojNCwOYAEhLjQM=
+github.com/golang/snappy v0.0.4/go.mod h1:/XxbfmMg8lxefKM7IXC3fBNl/7bRcc72aCRzEWrmP2Q=
+github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
+github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+google.golang.org/protobuf v1.26.0-rc.1/go.mod h1:jlhhOSvTdKEhbULTjvd4ARK9grFBp09yW+WbY/TyQbw=
+google.golang.org/protobuf v1.26.0 h1:bxAC2xTBsZGibn2RTntX0oH50xLsqy1OxA9tTL3p/lk=
+google.golang.org/protobuf v1.26.0/go.mod h1:9q0QmTI4eRPtz6boOQmLYwt+qCgq0jsYwAQnmE0givc=
diff --git a/promtail/common.go b/promtail/common.go
index f44774d..21c4e54 100644
--- a/promtail/common.go
+++ b/promtail/common.go
@@ -31,6 +31,8 @@ type ClientConfig struct {
 	SendLevel LogLevel
 	// Logs are printed to stdout if the entry level is >= PrintLevel
 	PrintLevel LogLevel
+	// fmt string to express the prefix
+	PrefixFormat string
 }
 
 type Client interface {
@@ -67,4 +69,4 @@ func (client *httpClient) sendJsonReq(method, url string, ctype string, reqBody
 	}
 
 	return resp, resBody, nil
-}
\ No newline at end of file
+}
diff --git a/promtail/jsonclient.go b/promtail/jsonclient.go
index 6ee022e..fbef7ae 100644
--- a/promtail/jsonclient.go
+++ b/promtail/jsonclient.go
@@ -11,7 +11,7 @@ import (
 type jsonLogEntry struct {
 	Ts    time.Time `json:"ts"`
 	Line  string    `json:"line"`
-	level LogLevel // not used in JSON
+	level LogLevel  // not used in JSON
 }
 
 type promtailStream struct {
@@ -24,19 +24,26 @@ type promtailMsg struct {
 }
 
 type clientJson struct {
-	config    *ClientConfig
-	quit      chan struct{}
-	entries   chan *jsonLogEntry
-	waitGroup sync.WaitGroup
-	client    httpClient
+	config       *ClientConfig
+	quit         chan struct{}
+	entries      chan *jsonLogEntry
+	waitGroup    sync.WaitGroup
+	client       httpClient
+	prefixFormat string
 }
 
 func NewClientJson(conf ClientConfig) (Client, error) {
+	prefixFormat := "%s: "
+	if conf.PrefixFormat != "" {
+		prefixFormat = conf.PrefixFormat
+	}
+
 	client := clientJson{
-		config:  &conf,
-		quit:    make(chan struct{}),
-		entries: make(chan *jsonLogEntry, LOG_ENTRIES_CHAN_SIZE),
-		client:  httpClient{},
+		config:       &conf,
+		quit:         make(chan struct{}),
+		entries:      make(chan *jsonLogEntry, LOG_ENTRIES_CHAN_SIZE),
+		client:       httpClient{},
+		prefixFormat: prefixFormat,
 	}
 
 	client.waitGroup.Add(1)
@@ -46,19 +53,23 @@ func NewClientJson(conf ClientConfig) (Client, error) {
 }
 
 func (c *clientJson) Debugf(format string, args ...interface{}) {
-	c.log(format, DEBUG, "Debug: ", args...)
+	prefix := fmt.Sprintf(c.prefixFormat, "Debug")
+	c.log(format, DEBUG, prefix, args...)
 }
 
 func (c *clientJson) Infof(format string, args ...interface{}) {
-	c.log(format, INFO, "Info: ", args...)
+	prefix := fmt.Sprintf(c.prefixFormat, "Info")
+	c.log(format, INFO, prefix, args...)
 }
 
 func (c *clientJson) Warnf(format string, args ...interface{}) {
-	c.log(format, WARN, "Warn: ", args...)
+	prefix := fmt.Sprintf(c.prefixFormat, "Warn")
+	c.log(format, WARN, prefix, args...)
 }
 
 func (c *clientJson) Errorf(format string, args ...interface{}) {
-	c.log(format, ERROR, "Error: ", args...)
+	prefix := fmt.Sprintf(c.prefixFormat, "Error")
+	c.log(format, ERROR, prefix, args...)
 }
 
 func (c *clientJson) log(format string, level LogLevel, prefix string, args ...interface{}) {
diff --git a/promtail/protoclient.go b/promtail/protoclient.go
index 6764e0f..db0adbc 100644
--- a/promtail/protoclient.go
+++ b/promtail/protoclient.go
@@ -2,10 +2,10 @@ package promtail
 
 import (
 	"fmt"
+	"github.com/afiskon/promtail-client/logproto"
 	"github.com/golang/protobuf/proto"
 	"github.com/golang/protobuf/ptypes/timestamp"
 	"github.com/golang/snappy"
-	"github.com/afiskon/promtail-client/logproto"
 	"log"
 	"sync"
 	"time"
@@ -17,19 +17,26 @@ type protoLogEntry struct {
 }
 
 type clientProto struct {
-	config    *ClientConfig
-	quit      chan struct{}
-	entries   chan protoLogEntry
-	waitGroup sync.WaitGroup
-	client    httpClient
+	config       *ClientConfig
+	quit         chan struct{}
+	entries      chan protoLogEntry
+	waitGroup    sync.WaitGroup
+	client       httpClient
+	prefixFormat string
 }
 
 func NewClientProto(conf ClientConfig) (Client, error) {
+	prefixFormat := "%s: "
+	if conf.PrefixFormat != "" {
+		prefixFormat = conf.PrefixFormat
+	}
+
 	client := clientProto{
-		config:  &conf,
-		quit:    make(chan struct{}),
-		entries: make(chan protoLogEntry, LOG_ENTRIES_CHAN_SIZE),
-		client:  httpClient{},
+		config:       &conf,
+		quit:         make(chan struct{}),
+		entries:      make(chan protoLogEntry, LOG_ENTRIES_CHAN_SIZE),
+		client:       httpClient{},
+		prefixFormat: prefixFormat,
 	}
 
 	client.waitGroup.Add(1)
@@ -39,19 +46,23 @@ func NewClientProto(conf ClientConfig) (Client, error) {
 }
 
 func (c *clientProto) Debugf(format string, args ...interface{}) {
-	c.log(format, DEBUG, "Debug: ", args...)
+	prefix := fmt.Sprintf(c.prefixFormat, "Debug")
+	c.log(format, DEBUG, prefix, args...)
 }
 
 func (c *clientProto) Infof(format string, args ...interface{}) {
-	c.log(format, INFO, "Info: ", args...)
+	prefix := fmt.Sprintf(c.prefixFormat, "Info")
+	c.log(format, INFO, prefix, args...)
 }
 
 func (c *clientProto) Warnf(format string, args ...interface{}) {
-	c.log(format, WARN, "Warn: ", args...)
+	prefix := fmt.Sprintf(c.prefixFormat, "Warn")
+	c.log(format, WARN, prefix, args...)
 }
 
 func (c *clientProto) Errorf(format string, args ...interface{}) {
-	c.log(format, ERROR, "Error: ", args...)
+	prefix := fmt.Sprintf(c.prefixFormat, "Error")
+	c.log(format, ERROR, prefix, args...)
 }
 
 func (c *clientProto) log(format string, level LogLevel, prefix string, args ...interface{}) {