diff --git a/pkg/errs/account.go b/pkg/errs/account.go
index bb8131a4..4f65a4fb 100644
--- a/pkg/errs/account.go
+++ b/pkg/errs/account.go
@@ -2,6 +2,7 @@ package errs
 
 import "net/http"
 
+// Error codes related to accounts
 var (
 	ErrAccountIdInvalid                       = NewNormalError(NORMAL_SUBCATEGORY_ACCOUNT, 0, http.StatusBadRequest, "account id is invalid")
 	ErrAccountNotFound                        = NewNormalError(NORMAL_SUBCATEGORY_ACCOUNT, 1, http.StatusBadRequest, "account not found")
diff --git a/pkg/errs/database.go b/pkg/errs/database.go
index 170257a2..4705046a 100644
--- a/pkg/errs/database.go
+++ b/pkg/errs/database.go
@@ -4,6 +4,7 @@ import (
 	"net/http"
 )
 
+// Error codes related to database
 var (
 	ErrDatabaseTypeInvalid     = NewSystemError(SYSTEM_SUBCATEGORY_DATABASE, 0, http.StatusInternalServerError, "database type is invalid")
 	ErrDatabaseHostInvalid     = NewSystemError(SYSTEM_SUBCATEGORY_DATABASE, 1, http.StatusInternalServerError, "database host is invalid")
diff --git a/pkg/errs/error.go b/pkg/errs/error.go
index 63742895..569c1ec9 100644
--- a/pkg/errs/error.go
+++ b/pkg/errs/error.go
@@ -1,15 +1,23 @@
 package errs
 
+// ErrorCategory represents error category
 type ErrorCategory int
 
+// Error categories
 const (
 	CATEGORY_SYSTEM ErrorCategory = 1
 	CATEGORY_NORMAL ErrorCategory = 2
+)
 
+// Sub categories of system error
+const (
 	SYSTEM_SUBCATEGORY_DEFAULT  = 0
 	SYSTEM_SUBCATEGORY_SETTING  = 1
 	SYSTEM_SUBCATEGORY_DATABASE = 2
+)
 
+// Sub categories of normal error
+const (
 	NORMAL_SUBCATEGORY_GLOBAL      = 0
 	NORMAL_SUBCATEGORY_USER        = 1
 	NORMAL_SUBCATEGORY_TOKEN       = 2
@@ -20,6 +28,7 @@ const (
 	NORMAL_SUBCATEGORY_TAG         = 7
 )
 
+// Error represents the specific error returned to user
 type Error struct {
 	Category       ErrorCategory
 	SubCategory    int
@@ -29,14 +38,17 @@ type Error struct {
 	BaseError      []error
 }
 
+// Error returns the error message
 func (err *Error) Error() string {
 	return err.Message
 }
 
+// Code returns the error code
 func (err *Error) Code() int {
 	return int(err.Category)*100000 + err.SubCategory*1000 + err.Index
 }
 
+// New returns a new error instance
 func New(category ErrorCategory, subCategory int, index int, httpStatusCode int, message string, baseError ...error) *Error {
 	return &Error{
 		Category:       category,
@@ -48,14 +60,17 @@ func New(category ErrorCategory, subCategory int, index int, httpStatusCode int,
 	}
 }
 
+// NewSystemError returns a new system error instance
 func NewSystemError(subCategory int, index int, httpStatusCode int, message string) *Error {
 	return New(CATEGORY_SYSTEM, subCategory, index, httpStatusCode, message)
 }
 
+// NewNormalError returns a new normal error instance
 func NewNormalError(subCategory int, index int, httpStatusCode int, message string) *Error {
 	return New(CATEGORY_NORMAL, subCategory, index, httpStatusCode, message)
 }
 
+// NewIncompleteOrIncorrectSubmissionError returns a new incomplete or incorrect submission error instance
 func NewIncompleteOrIncorrectSubmissionError(err error) *Error {
 	return New(ErrIncompleteOrIncorrectSubmission.Category,
 		ErrIncompleteOrIncorrectSubmission.SubCategory,
@@ -64,6 +79,8 @@ func NewIncompleteOrIncorrectSubmissionError(err error) *Error {
 		ErrIncompleteOrIncorrectSubmission.Message, err)
 }
 
+// Or would return the error from err parameter if the this error is defined in this project,
+// or return the default error
 func Or(err error, defaultErr *Error) *Error {
 	if finalError, ok := err.(*Error); ok {
 		return finalError
@@ -72,6 +89,7 @@ func Or(err error, defaultErr *Error) *Error {
 	}
 }
 
+// IsCustomError returns whether this error is defined in this project
 func IsCustomError(err error) bool {
 	_, ok := err.(*Error)
 	return ok
diff --git a/pkg/errs/global.go b/pkg/errs/global.go
index 28b69d53..ea538bf9 100644
--- a/pkg/errs/global.go
+++ b/pkg/errs/global.go
@@ -5,6 +5,7 @@ import (
 	"net/http"
 )
 
+// General error codes
 var (
 	ErrIncompleteOrIncorrectSubmission = NewNormalError(NORMAL_SUBCATEGORY_GLOBAL, 0, http.StatusBadRequest, "incomplete or incorrect submission")
 	ErrOperationFailed                 = NewNormalError(NORMAL_SUBCATEGORY_GLOBAL, 1, http.StatusInternalServerError, "operation failed")
@@ -16,50 +17,62 @@ var (
 	ErrPageCountInvalid                = NewNormalError(NORMAL_SUBCATEGORY_GLOBAL, 7, http.StatusBadRequest, "page count is invalid")
 )
 
+// GetParameterInvalidMessage returns specific error message for invalid parameter error
 func GetParameterInvalidMessage(field string) string {
 	return fmt.Sprintf("parameter \"%s\" is invalid", field)
 }
 
+// GetParameterIsRequiredMessage returns specific error message for missing parameter error
 func GetParameterIsRequiredMessage(field string) string {
 	return fmt.Sprintf("parameter \"%s\" is required", field)
 }
 
+// GetParameterMustLessThanMessage returns specific error message for parameter too large error
 func GetParameterMustLessThanMessage(field string, param string) string {
 	return fmt.Sprintf("parameter \"%s\" must be less than %s", field, param)
 }
 
+// GetParameterMustLessThanCharsMessage returns specific error message for parameter too long error
 func GetParameterMustLessThanCharsMessage(field string, param string) string {
 	return fmt.Sprintf("parameter \"%s\" must be less than %s characters", field, param)
 }
 
+// GetParameterMustMoreThanMessage returns specific error message for parameter too small error
 func GetParameterMustMoreThanMessage(field string, param string) string {
 	return fmt.Sprintf("parameter \"%s\" must be more than %s", field, param)
 }
 
+// GetParameterMustMoreThanCharsMessage returns specific error message for parameter too short error
 func GetParameterMustMoreThanCharsMessage(field string, param string) string {
 	return fmt.Sprintf("parameter \"%s\" must be more than %s characters", field, param)
 }
 
+// GetParameterLengthNotEqualMessage returns specific error message for parameter length wrong error
 func GetParameterLengthNotEqualMessage(field string, param string) string {
 	return fmt.Sprintf("parameter \"%s\" length is not equal to %s", field, param)
 }
 
+// GetParameterNotBeBlankMessage returns specific error message for blank parameter error
 func GetParameterNotBeBlankMessage(field string) string {
 	return fmt.Sprintf("parameter \"%s\" cannot be blank", field)
 }
 
+// GetParameterInvalidUsernameMessage returns specific error message for invalid username parameter error
 func GetParameterInvalidUsernameMessage(field string) string {
 	return fmt.Sprintf("parameter \"%s\" is invalid username format", field)
 }
 
+// GetParameterInvalidEmailMessage returns specific error message for invalid email parameter error
 func GetParameterInvalidEmailMessage(field string) string {
 	return fmt.Sprintf("parameter \"%s\" is invalid email format", field)
 }
 
+// GetParameterInvalidCurrencyMessage returns specific error message for invalid currency parameter error
 func GetParameterInvalidCurrencyMessage(field string) string {
 	return fmt.Sprintf("parameter \"%s\" is invalid currency", field)
 }
 
+// GetParameterInvalidHexRGBColorMessage returns specific error message for invalid hex rgb color parameter error
 func GetParameterInvalidHexRGBColorMessage(field string) string {
 	return fmt.Sprintf("parameter \"%s\" is invalid color", field)
 }
diff --git a/pkg/errs/setting.go b/pkg/errs/setting.go
index 17d3d876..f047498b 100644
--- a/pkg/errs/setting.go
+++ b/pkg/errs/setting.go
@@ -2,6 +2,7 @@ package errs
 
 import "net/http"
 
+// Error codes related to settings
 var (
 	ErrInvalidProtocol     = NewSystemError(SYSTEM_SUBCATEGORY_SETTING, 0, http.StatusInternalServerError, "invalid server protocol")
 	ErrInvalidLogMode      = NewSystemError(SYSTEM_SUBCATEGORY_SETTING, 1, http.StatusInternalServerError, "invalid log mode")
diff --git a/pkg/errs/system.go b/pkg/errs/system.go
index 2b4fdccd..c575863b 100644
--- a/pkg/errs/system.go
+++ b/pkg/errs/system.go
@@ -2,6 +2,7 @@ package errs
 
 import "net/http"
 
+// Error codes related to transaction categories
 var (
 	ErrSystemError      = NewSystemError(SYSTEM_SUBCATEGORY_DEFAULT, 0, http.StatusInternalServerError, "system error")
 	ErrApiNotFound      = NewSystemError(SYSTEM_SUBCATEGORY_DEFAULT, 1, http.StatusNotFound, "api not found")
diff --git a/pkg/errs/token.go b/pkg/errs/token.go
index 50f1d0ee..2a4e18ac 100644
--- a/pkg/errs/token.go
+++ b/pkg/errs/token.go
@@ -4,6 +4,7 @@ import (
 	"net/http"
 )
 
+// Error codes related to tokens
 var (
 	ErrTokenGenerating           = NewNormalError(NORMAL_SUBCATEGORY_TOKEN, 0, http.StatusInternalServerError, "failed to generate token")
 	ErrUnauthorizedAccess        = NewNormalError(NORMAL_SUBCATEGORY_TOKEN, 1, http.StatusUnauthorized, "unauthorized access")
diff --git a/pkg/errs/transaction.go b/pkg/errs/transaction.go
index c39333b0..d9d18338 100644
--- a/pkg/errs/transaction.go
+++ b/pkg/errs/transaction.go
@@ -2,6 +2,7 @@ package errs
 
 import "net/http"
 
+// Error codes related to transaction
 var (
 	ErrTransactionIdInvalid                                = NewNormalError(NORMAL_SUBCATEGORY_TRANSACTION, 0, http.StatusBadRequest, "transaction id is invalid")
 	ErrTransactionNotFound                                 = NewNormalError(NORMAL_SUBCATEGORY_TRANSACTION, 1, http.StatusBadRequest, "transaction not found")
diff --git a/pkg/errs/transaction_category.go b/pkg/errs/transaction_category.go
index 3f6293b4..147515b0 100644
--- a/pkg/errs/transaction_category.go
+++ b/pkg/errs/transaction_category.go
@@ -2,6 +2,7 @@ package errs
 
 import "net/http"
 
+// Error codes related to transaction categories
 var (
 	ErrTransactionCategoryIdInvalid            = NewNormalError(NORMAL_SUBCATEGORY_CATEGORY, 0, http.StatusBadRequest, "transaction category id is invalid")
 	ErrTransactionCategoryNotFound             = NewNormalError(NORMAL_SUBCATEGORY_CATEGORY, 1, http.StatusBadRequest, "transaction category not found")
diff --git a/pkg/errs/transaction_tag.go b/pkg/errs/transaction_tag.go
index ae3f615c..47460fc2 100644
--- a/pkg/errs/transaction_tag.go
+++ b/pkg/errs/transaction_tag.go
@@ -2,6 +2,7 @@ package errs
 
 import "net/http"
 
+// Error codes related to transaction tags
 var (
 	ErrTransactionTagIdInvalid            = NewNormalError(NORMAL_SUBCATEGORY_TAG, 0, http.StatusBadRequest, "transaction tag id is invalid")
 	ErrTransactionTagNotFound             = NewNormalError(NORMAL_SUBCATEGORY_TAG, 1, http.StatusBadRequest, "transaction tag not found")
diff --git a/pkg/errs/twofactor_authorization.go b/pkg/errs/twofactor_authorization.go
index f4b4ff46..c49197a7 100644
--- a/pkg/errs/twofactor_authorization.go
+++ b/pkg/errs/twofactor_authorization.go
@@ -2,6 +2,7 @@ package errs
 
 import "net/http"
 
+// Error codes related to two factor authorization
 var (
 	ErrPasscodeInvalid               = NewNormalError(NORMAL_SUBCATEGORY_TWOFACTOR, 0, http.StatusUnauthorized, "passcode is invalid")
 	ErrTwoFactorRecoveryCodeInvalid  = NewNormalError(NORMAL_SUBCATEGORY_TWOFACTOR, 1, http.StatusUnauthorized, "two factor backup code is invalid")
diff --git a/pkg/errs/user.go b/pkg/errs/user.go
index d82cd7a9..2c6f3b03 100644
--- a/pkg/errs/user.go
+++ b/pkg/errs/user.go
@@ -4,6 +4,7 @@ import (
 	"net/http"
 )
 
+// Error codes related to users
 var (
 	ErrLoginNameInvalid           = NewNormalError(NORMAL_SUBCATEGORY_USER, 0, http.StatusUnauthorized, "login name is invalid")
 	ErrLoginNameOrPasswordInvalid = NewNormalError(NORMAL_SUBCATEGORY_USER, 1, http.StatusUnauthorized, "login name or password is invalid")