diff --git a/formatter.go b/formatter.go
index 2d9ebba..f42fe86 100644
--- a/formatter.go
+++ b/formatter.go
@@ -14,6 +14,7 @@ type Formatter interface {
 type simpleFormatter struct {
 }
 
+// Format implements log.Formatter
 func (f simpleFormatter) Format(level Level, msg string, logger *Logger) []byte {
 	time := time.Now().Format("15:04:05.000")
 	return []byte(fmt.Sprintf("%s %s %s\n", time, level.String(), msg))
diff --git a/formatters/util_fileline.go b/formatters/util_fileline.go
index 9288439..3f2b3c3 100644
--- a/formatters/util_fileline.go
+++ b/formatters/util_fileline.go
@@ -5,6 +5,7 @@ import (
 	"strings"
 )
 
+// FilelineCaller returns file and line for caller
 func FilelineCaller(skip int) (file string, line int) {
 	for i := 0; i < 10; i++ {
 		_, file, line, ok := runtime.Caller(skip + i)
diff --git a/formatters/util_terminal.go b/formatters/util_terminal.go
index 2008e22..ab402b8 100644
--- a/formatters/util_terminal.go
+++ b/formatters/util_terminal.go
@@ -7,6 +7,7 @@ import (
 	"golang.org/x/crypto/ssh/terminal"
 )
 
+// IsTerminal returns whether is a valid tty for io.Writer
 func IsTerminal(w io.Writer) bool {
 	switch v := w.(type) {
 	case *os.File:
diff --git a/log.go b/log.go
index 004e5ad..ac7d8fd 100644
--- a/log.go
+++ b/log.go
@@ -3,147 +3,147 @@ package log
 // Default is a default Logger instance
 var Default = New()
 
-// Indicate whether output debug message
+// IsDebugEnabled indicates whether output message
 func IsDebugEnabled() bool {
 	return Default.IsDebugEnabled()
 }
 
-// Indicate whether output info message
+// IsInfoEnabled indicates whether output message
 func IsInfoEnabled() bool {
 	return Default.IsInfoEnabled()
 }
 
-// Indicate whether output info message
+// IsPrintEnabled indicates whether output message
 func IsPrintEnabled() bool {
 	return Default.IsPrintEnabled()
 }
 
-// Indicate whether output warning message
+// IsWarnEnabled indicates whether output message
 func IsWarnEnabled() bool {
 	return Default.IsWarnEnabled()
 }
 
-// Indicate whether output error message
+// IsErrorEnabled indicates whether output message
 func IsErrorEnabled() bool {
 	return Default.IsErrorEnabled()
 }
 
-// Indicate whether output panic message
+// IsPanicEnabled indicates whether output message
 func IsPanicEnabled() bool {
 	return Default.IsPanicEnabled()
 }
 
-// Indicate whether output fatal message
+// IsFatalEnabled indicates whether output message
 func IsFatalEnabled() bool {
 	return Default.IsFatalEnabled()
 }
 
-// Indicate whether output is off
+// IsDisabled indicates whether output message
 func IsDisabled() bool {
 	return Default.IsDisabled()
 }
 
-// Output a debug message
+// Debug outputs message, Arguments are handled by fmt.Sprint
 func Debug(obj ...interface{}) {
 	Default.Debug(obj...)
 }
 
-// Output an info message
+// Info outputs message, Arguments are handled by fmt.Sprint
 func Info(obj ...interface{}) {
 	Default.Info(obj...)
 }
 
-// Output an info message
+// Print outputs message, Arguments are handled by fmt.Sprint
 func Print(obj ...interface{}) {
 	Default.Print(obj...)
 }
 
-// Output a warning message
+// Warn outputs message, Arguments are handled by fmt.Sprint
 func Warn(obj ...interface{}) {
 	Default.Warn(obj...)
 }
 
-// Output an error message
+// Error outputs message, Arguments are handled by fmt.Sprint
 func Error(obj ...interface{}) {
 	Default.Error(obj...)
 }
 
-// Output a panic message with full stack
+// Panic outputs message, and followed by a call to panic() Arguments are handled by fmt.Sprint
 func Panic(obj ...interface{}) {
 	Default.Panic(obj...)
 }
 
-// Output a fatal message with full stack
+// Fatal outputs message, and followed by a call to os.Exit(1) Arguments are handled by fmt.Sprint
 func Fatal(obj ...interface{}) {
 	Default.Fatal(obj...)
 }
 
-// Output a debug message
+// Debugln outputs message, Arguments are handled by fmt.Sprintln
 func Debugln(obj ...interface{}) {
 	Default.Debugln(obj...)
 }
 
-// Output an info message
+// Infoln outputs message, Arguments are handled by fmt.Sprintln
 func Infoln(obj ...interface{}) {
 	Default.Infoln(obj...)
 }
 
-// Output an info message
+// Println outputs message, Arguments are handled by fmt.Sprintln
 func Println(obj ...interface{}) {
 	Default.Println(obj...)
 }
 
-// Output a warning message
+// Warnln outputs message, Arguments are handled by fmt.Sprintln
 func Warnln(obj ...interface{}) {
 	Default.Warnln(obj...)
 }
 
-// Output an error message
+// Errorln outputs message, Arguments are handled by fmt.Sprintln
 func Errorln(obj ...interface{}) {
 	Default.Errorln(obj...)
 }
 
-// Output a panic message with full stack
+// Panicln outputs message and followed by a call to panic(), Arguments are handled by fmt.Sprintln
 func Panicln(obj ...interface{}) {
 	Default.Panicln(obj...)
 }
 
-// Output a fatal message with full stack
+// Fatalln outputs message and followed by a call to os.Exit(1), Arguments are handled by fmt.Sprintln
 func Fatalln(obj ...interface{}) {
 	Default.Fatalln(obj...)
 }
 
-// Output a debug message
+// Debugf outputs message, Arguments are handled by fmt.Sprintf
 func Debugf(msg string, args ...interface{}) {
 	Default.Debugf(msg, args...)
 }
 
-// Output an info message
+// Infof outputs message, Arguments are handled by fmt.Sprintf
 func Infof(msg string, args ...interface{}) {
 	Default.Infof(msg, args...)
 }
 
-// Output an info message
+// Printf outputs message, Arguments are handled by fmt.Sprintf
 func Printf(msg string, args ...interface{}) {
 	Default.Printf(msg, args...)
 }
 
-// Output a warning message
+// Warnf outputs message, Arguments are handled by fmt.Sprintf
 func Warnf(msg string, args ...interface{}) {
 	Default.Warnf(msg, args...)
 }
 
-// Output an error message
+// Errorf outputs message, Arguments are handled by fmt.Sprintf
 func Errorf(msg string, args ...interface{}) {
 	Default.Errorf(msg, args...)
 }
 
-// Output a panic message with full stack
+// Panicf outputs message and followed by a call to panic(), Arguments are handled by fmt.Sprintf
 func Panicf(msg string, args ...interface{}) {
 	Default.Panicf(msg, args...)
 }
 
-// Output a fatal message with full stack
+// Fatalf outputs message and followed by a call to os.Exit(1), Arguments are handled by fmt.Sprintf
 func Fatalf(msg string, args ...interface{}) {
 	Default.Fatalf(msg, args...)
 }
diff --git a/logger.go b/logger.go
index 5ef292b..11efda4 100644
--- a/logger.go
+++ b/logger.go
@@ -7,8 +7,10 @@ import (
 	"sync"
 )
 
+// Exit is equals os.Exit
 var Exit = os.Exit
 
+// Logger is represents an active logging object
 type Logger struct {
 	m         sync.Mutex
 	Level     Level
@@ -16,6 +18,7 @@ type Logger struct {
 	Out       io.Writer
 }
 
+// New creates a new Logger
 func New() *Logger {
 	return &Logger{
 		Level:     INFO,
@@ -24,68 +27,82 @@ func New() *Logger {
 	}
 }
 
+// IsDebugEnabled indicates whether output message
 func (l *Logger) IsDebugEnabled() bool {
 	return l.Level >= DEBUG
 }
 
+// IsInfoEnabled indicates whether output message
 func (l *Logger) IsInfoEnabled() bool {
 	return l.Level >= INFO
 }
 
+// IsPrintEnabled indicates whether output message
 func (l *Logger) IsPrintEnabled() bool {
 	return l.Level > OFF
 }
 
+// IsWarnEnabled indicates whether output message
 func (l *Logger) IsWarnEnabled() bool {
 	return l.Level >= WARN
 }
 
+// IsErrorEnabled indicates whether output message
 func (l *Logger) IsErrorEnabled() bool {
 	return l.Level >= ERROR
 }
 
+// IsPanicEnabled indicates whether output message
 func (l *Logger) IsPanicEnabled() bool {
 	return l.Level >= PANIC
 }
 
+// IsFatalEnabled indicates whether output message
 func (l *Logger) IsFatalEnabled() bool {
 	return l.Level >= FATAL
 }
 
+// IsDisabled indicates whether output message
 func (l *Logger) IsDisabled() bool {
 	return l.Level <= OFF
 }
 
+// Debug outputs message, Arguments are handled by fmt.Sprint
 func (l *Logger) Debug(obj ...interface{}) {
 	if l.Level >= DEBUG {
 		l.log(DEBUG, fmt.Sprint(obj...))
 	}
 }
 
+// Info outputs message, Arguments are handled by fmt.Sprint
 func (l *Logger) Info(obj ...interface{}) {
 	if l.Level >= INFO {
 		l.log(INFO, fmt.Sprint(obj...))
 	}
 }
 
+// Print outputs message, Arguments are handled by fmt.Sprint
 func (l *Logger) Print(obj ...interface{}) {
 	if l.Level != OFF {
 		l.log(INFO, fmt.Sprint(obj...))
 	}
 }
 
+// Warn outputs message, Arguments are handled by fmt.Sprint
 func (l *Logger) Warn(obj ...interface{}) {
 	if l.Level >= WARN {
 		l.log(WARN, fmt.Sprint(obj...))
 	}
 }
 
+// Error outputs message, Arguments are handled by fmt.Sprint
 func (l *Logger) Error(obj ...interface{}) {
 	if l.Level >= ERROR {
 		l.log(ERROR, fmt.Sprint(obj...))
 	}
 }
 
+// Panic outputs message, and followed by a call to panic() Arguments are handled by fmt.Sprint
 func (l *Logger) Panic(obj ...interface{}) {
 	if l.Level >= PANIC {
 		l.log(PANIC, fmt.Sprint(obj...))
@@ -93,6 +110,7 @@ func (l *Logger) Panic(obj ...interface{}) {
 	panic(fmt.Sprint(obj...))
 }
 
+// Fatal outputs message and followed by a call to os.Exit(1), Arguments are handled by fmt.Sprint
 func (l *Logger) Fatal(obj ...interface{}) {
 	if l.Level >= FATAL {
 		l.log(FATAL, fmt.Sprint(obj...))
@@ -100,36 +118,42 @@ func (l *Logger) Fatal(obj ...interface{}) {
 	Exit(1)
 }
 
+// Debugln outputs message, Arguments are handled by fmt.Sprintln
 func (l *Logger) Debugln(obj ...interface{}) {
 	if l.Level >= DEBUG {
 		l.log(DEBUG, vsprintln(obj...))
 	}
 }
 
+// Infoln outputs message, Arguments are handled by fmt.Sprintln
 func (l *Logger) Infoln(obj ...interface{}) {
 	if l.Level >= INFO {
 		l.log(INFO, vsprintln(obj...))
 	}
 }
 
+// Println outputs message, Arguments are handled by fmt.Sprintln
 func (l *Logger) Println(obj ...interface{}) {
 	if l.Level != OFF {
 		l.log(INFO, vsprintln(obj...))
 	}
 }
 
+// Warnln outputs message, Arguments are handled by fmt.Sprintln
 func (l *Logger) Warnln(obj ...interface{}) {
 	if l.Level >= WARN {
 		l.log(WARN, vsprintln(obj...))
 	}
 }
 
+// Errorln outputs message, Arguments are handled by fmt.Sprintln
 func (l *Logger) Errorln(obj ...interface{}) {
 	if l.Level >= ERROR {
 		l.log(ERROR, vsprintln(obj...))
 	}
 }
 
+// Panicln outputs message and followed by a call to panic(), Arguments are handled by fmt.Sprintln
 func (l *Logger) Panicln(obj ...interface{}) {
 	if l.Level >= PANIC {
 		l.log(PANIC, vsprintln(obj...))
@@ -137,6 +161,7 @@ func (l *Logger) Panicln(obj ...interface{}) {
 	panic(vsprintln(obj...))
 }
 
+// Fatalln outputs message and followed by a call to os.Exit(1), Arguments are handled by fmt.Sprintln
 func (l *Logger) Fatalln(obj ...interface{}) {
 	if l.Level >= FATAL {
 		l.log(FATAL, vsprintln(obj...))
@@ -144,36 +169,42 @@ func (l *Logger) Fatalln(obj ...interface{}) {
 	Exit(1)
 }
 
+// Debugf outputs message, Arguments are handles by fmt.Sprintf
 func (l *Logger) Debugf(msg string, args ...interface{}) {
 	if l.Level >= DEBUG {
 		l.log(DEBUG, fmt.Sprintf(msg, args...))
 	}
 }
 
+// Infof outputs message, Arguments are handles by fmt.Sprintf
 func (l *Logger) Infof(msg string, args ...interface{}) {
 	if l.Level >= INFO {
 		l.log(INFO, fmt.Sprintf(msg, args...))
 	}
 }
 
+// Printf outputs message, Arguments are handles by fmt.Sprintf
 func (l *Logger) Printf(msg string, args ...interface{}) {
 	if l.Level != OFF {
 		l.log(INFO, fmt.Sprintf(msg, args...))
 	}
 }
 
+// Warnf outputs message, Arguments are handles by fmt.Sprintf
 func (l *Logger) Warnf(msg string, args ...interface{}) {
 	if l.Level >= WARN {
 		l.log(WARN, fmt.Sprintf(msg, args...))
 	}
 }
 
+// Errorf outputs message, Arguments are handles by fmt.Sprintf
 func (l *Logger) Errorf(msg string, args ...interface{}) {
 	if l.Level >= ERROR {
 		l.log(ERROR, fmt.Sprintf(msg, args...))
 	}
 }
 
+// Panicf outputs message and followed by a call to panic(), Arguments are handles by fmt.Sprintf
 func (l *Logger) Panicf(msg string, args ...interface{}) {
 	if l.Level >= PANIC {
 		l.log(PANIC, fmt.Sprintf(msg, args...))
@@ -181,6 +212,7 @@ func (l *Logger) Panicf(msg string, args ...interface{}) {
 	panic(fmt.Sprintf(msg, args...))
 }
 
+// Fatalf outputs message and followed by a call to os.Exit(1), Arguments are handles by fmt.Sprintf
 func (l *Logger) Fatalf(msg string, args ...interface{}) {
 	if l.Level >= FATAL {
 		l.log(FATAL, fmt.Sprintf(msg, args...))
diff --git a/writers/always_new_file_writer.go b/writers/always_new_file_writer.go
index b3e8d5b..8402538 100644
--- a/writers/always_new_file_writer.go
+++ b/writers/always_new_file_writer.go
@@ -19,6 +19,7 @@ type AlwaysNewFileWriter struct {
 	file *os.File
 }
 
+// Write implements io.Writer
 func (w *AlwaysNewFileWriter) Write(p []byte) (n int, err error) {
 	if w.file == nil {
 		w.openFile()
diff --git a/writers/daily_file_writer.go b/writers/daily_file_writer.go
index 8347386..72d21ca 100644
--- a/writers/daily_file_writer.go
+++ b/writers/daily_file_writer.go
@@ -20,6 +20,7 @@ type DailyFileWriter struct {
 	nextDayTime int64
 }
 
+// Write implements io.Writer
 func (w *DailyFileWriter) Write(p []byte) (n int, err error) {
 	now := time.Now()
 
diff --git a/writers/fixed_size_file_writer.go b/writers/fixed_size_file_writer.go
index 1070d42..b53fdbf 100644
--- a/writers/fixed_size_file_writer.go
+++ b/writers/fixed_size_file_writer.go
@@ -17,6 +17,7 @@ type FixedSizeFileWriter struct {
 	currentSize int64
 }
 
+// Write implements io.Writer
 func (w *FixedSizeFileWriter) Write(p []byte) (n int, err error) {
 	if w.file == nil {
 		w.openCurrentFile()