diff --git a/csv_writer.go b/csv_writer.go
index 82d8cf2..570df19 100644
--- a/csv_writer.go
+++ b/csv_writer.go
@@ -5,6 +5,7 @@ import (
 	"strings"
 )
 
+// CsvWriter writes data in csv format using FileWriter
 type CsvWriter struct {
 	fw        FileWriter
 	dstFile   string
@@ -12,6 +13,7 @@ type CsvWriter struct {
 	delimiter string
 }
 
+// NewCsvWriter builds new CsvWriter
 func NewCsvWriter(fw FileWriter, dstFile, dstDir, delimiter string) *CsvWriter {
 	return &CsvWriter{
 		fw,
@@ -21,10 +23,12 @@ func NewCsvWriter(fw FileWriter, dstFile, dstDir, delimiter string) *CsvWriter {
 	}
 }
 
+// WriteDDL is part of interface. It is not usefull for csv. 
 func (w *CsvWriter) WriteDDL(tableName string, ddl string) (err error) {
 	return
 }
 
+// WriteRows writes result rows in csv format
 func (w *CsvWriter) WriteRows(tableName string, columns []string, rows []*map[string]interface{}) (err error) {
 	f, err := w.fw.getFileHandler(w.getFilename(tableName))
 	if err != nil {
diff --git a/filewriter.go b/filewriter.go
index f58a2ce..fa7534c 100644
--- a/filewriter.go
+++ b/filewriter.go
@@ -5,19 +5,23 @@ import (
 	"os"
 )
 
+// File is interface which can writes strings to file
 type File interface {
 	WriteString(s string) (n int, err error)
 	Close() error
 }
 
+// FileWriter is interface which can instantiate File
 type FileWriter interface {
 	getFileHandler(filename string) (File, error)
 }
 
+// FileWriter writes files using filesystem and methods from OS
 type OsFileWriter struct {
 	openFiles map[string]bool
 }
 
+// NewOsFileWriter builds new OsFileWriter
 func NewOsFileWriter() *OsFileWriter {
 	return &OsFileWriter{
 		make(map[string]bool, 0),
diff --git a/query.go b/query.go
index d449c4e..930c61b 100644
--- a/query.go
+++ b/query.go
@@ -37,6 +37,7 @@ type ConnectionSettings struct {
 	dbhost   string
 }
 
+// TableColumnDDL represents result row from DESCRIBE command
 type TableColumnDDL struct {
 	Field   string         `db:"Field"`
 	Type    string         `db:"Type"`
@@ -46,6 +47,7 @@ type TableColumnDDL struct {
 	Extra   string         `db:"Extra"`
 }
 
+// Result contains DDL and rows which were got from DB
 type Result struct {
 	DDL  *map[string]string
 	Rows *map[string]([]*map[string]interface{})
diff --git a/run.go b/run.go
index efec7d7..67f4d3d 100644
--- a/run.go
+++ b/run.go
@@ -6,6 +6,7 @@ import (
 	"os"
 )
 
+// Run is entry point for application
 func Run(dbConnect dbConnector, argsTail []string, configFile string, format string, fw FileWriter, dstFile string, dstDir string, csvDelimiter string) (err error) {
 	if len(argsTail) != 2 && len(argsTail) != 3 {
 		showHelp()
diff --git a/sql_writer.go b/sql_writer.go
index 0afc79f..bfa1818 100644
--- a/sql_writer.go
+++ b/sql_writer.go
@@ -5,12 +5,14 @@ import (
 	"strings"
 )
 
+// SqlWriter writes data in sql format using FileWriter
 type SqlWriter struct {
 	fw      FileWriter
 	dstFile string
 	dstDir  string
 }
 
+// NewSqlWriter builds new SqlWriter
 func NewSqlWriter(fw FileWriter, dstFile, dstDir string) *SqlWriter {
 	return &SqlWriter{
 		fw,
@@ -19,6 +21,7 @@ func NewSqlWriter(fw FileWriter, dstFile, dstDir string) *SqlWriter {
 	}
 }
 
+// WriteDDL writes SQL-query which creates tables - DDL
 func (w *SqlWriter) WriteDDL(tableName string, ddl string) (err error) {
 	contents := "SET FOREIGN_KEY_CHECKS=0;\n"
 	contents += ddl + "\n"
@@ -35,6 +38,7 @@ func (w *SqlWriter) WriteDDL(tableName string, ddl string) (err error) {
 	return
 }
 
+// WriteRows writes result rows in sql-insert format
 func (w *SqlWriter) WriteRows(tableName string, columns []string, rows []*map[string]interface{}) (err error) {
 	f, err := w.fw.getFileHandler(w.getFilename(tableName))
 	if err != nil {
diff --git a/writer.go b/writer.go
index 3688dd6..54b0e31 100644
--- a/writer.go
+++ b/writer.go
@@ -4,14 +4,17 @@ import (
 	"fmt"
 )
 
+// DataWriter is interface which can write result somewhere
 type DataWriter interface {
 	WriteRows(tableName string, columns []string, results []*map[string]interface{}) (err error)
 	WriteDDL(tableName string, ddl string) (err error)
 }
 
+// SimpleWriter writes result into stdout using simple format (concatinated values)
 type SimpleWriter struct {
 }
 
+// WriteRows prints result rows in simple format (concatinated values) into stdout
 func (w *SimpleWriter) WriteRows(tableName string, _ []string, rows []*map[string]interface{}) (err error) {
 	fmt.Println(tableName)
 	for _, row := range rows {
@@ -44,6 +47,7 @@ func (w *SimpleWriter) WriteRows(tableName string, _ []string, rows []*map[strin
 	return nil
 }
 
+// WriteDDL prints DDL as is into stdout
 func (w *SimpleWriter) WriteDDL(tableName string, ddl string) (err error) {
 	fmt.Println(ddl)
 	return nil