Programming language: Go
License: MIT License
Tags: Validation    
Latest version: v0.0.1

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A package of validators and sanitizers for strings, structs and collections. Based on validator.js.


Make sure that Go is installed on your computer. Type the following command in your terminal:

go get github.com/asaskevich/govalidator

or you can get specified release of the package with gopkg.in:

go get gopkg.in/asaskevich/govalidator.v10

After it the package is ready to use.

Import package in your project

Add following line in your *.go file:

import "github.com/asaskevich/govalidator"

If you are unhappy to use long govalidator, you can do something like this:

import (
  valid "github.com/asaskevich/govalidator"
Activate behavior to require all fields have a validation tag by default

SetFieldsRequiredByDefault causes validation to fail when struct fields do not include validations or are not explicitly marked as exempt (using valid:"-" or valid:"email,optional"). A good place to activate this is a package init function or the main() function.

SetNilPtrAllowedByRequired causes validation to pass when struct fields marked by required are set to nil. This is disabled by default for consistency, but some packages that need to be able to determine between nil and zero value state can use this. If disabled, both nil and zero values cause validation errors.

import "github.com/asaskevich/govalidator"

func init() {

Here's some code to explain it:

// this struct definition will fail govalidator.ValidateStruct() (and the field values do not matter):
type exampleStruct struct {
  Name  string ``
  Email string `valid:"email"`

// this, however, will only fail when Email is empty or an invalid email address:
type exampleStruct2 struct {
  Name  string `valid:"-"`
  Email string `valid:"email"`

// lastly, this will only fail when Email is an invalid email address but not when it's empty:
type exampleStruct2 struct {
  Name  string `valid:"-"`
  Email string `valid:"email,optional"`
Recent breaking changes (see #123)
Custom validator function signature

A context was added as the second parameter, for structs this is the object being validated – this makes dependent validation possible.

import "github.com/asaskevich/govalidator"

// old signature
func(i interface{}) bool

// new signature
func(i interface{}, o interface{}) bool
Adding a custom validator

This was changed to prevent data races when accessing custom validators.

import "github.com/asaskevich/govalidator"

// before
govalidator.CustomTypeTagMap["customByteArrayValidator"] = func(i interface{}, o interface{}) bool {
  // ...

// after
govalidator.CustomTypeTagMap.Set("customByteArrayValidator", func(i interface{}, o interface{}) bool {
  // ...
List of functions:
func Abs(value float64) float64
func BlackList(str, chars string) string
func ByteLength(str string, params ...string) bool
func CamelCaseToUnderscore(str string) string
func Contains(str, substring string) bool
func Count(array []interface{}, iterator ConditionIterator) int
func Each(array []interface{}, iterator Iterator)
func ErrorByField(e error, field string) string
func ErrorsByField(e error) map[string]string
func Filter(array []interface{}, iterator ConditionIterator) []interface{}
func Find(array []interface{}, iterator ConditionIterator) interface{}
func GetLine(s string, index int) (string, error)
func GetLines(s string) []string
func HasLowerCase(str string) bool
func HasUpperCase(str string) bool
func HasWhitespace(str string) bool
func HasWhitespaceOnly(str string) bool
func InRange(value interface{}, left interface{}, right interface{}) bool
func InRangeFloat32(value, left, right float32) bool
func InRangeFloat64(value, left, right float64) bool
func InRangeInt(value, left, right interface{}) bool
func IsASCII(str string) bool
func IsAlpha(str string) bool
func IsAlphanumeric(str string) bool
func IsBase64(str string) bool
func IsByteLength(str string, min, max int) bool
func IsCIDR(str string) bool
func IsCRC32(str string) bool
func IsCRC32b(str string) bool
func IsCreditCard(str string) bool
func IsDNSName(str string) bool
func IsDataURI(str string) bool
func IsDialString(str string) bool
func IsDivisibleBy(str, num string) bool
func IsEmail(str string) bool
func IsExistingEmail(email string) bool
func IsFilePath(str string) (bool, int)
func IsFloat(str string) bool
func IsFullWidth(str string) bool
func IsHalfWidth(str string) bool
func IsHash(str string, algorithm string) bool
func IsHexadecimal(str string) bool
func IsHexcolor(str string) bool
func IsHost(str string) bool
func IsIP(str string) bool
func IsIPv4(str string) bool
func IsIPv6(str string) bool
func IsISBN(str string, version int) bool
func IsISBN10(str string) bool
func IsISBN13(str string) bool
func IsISO3166Alpha2(str string) bool
func IsISO3166Alpha3(str string) bool
func IsISO4217(str string) bool
func IsISO693Alpha2(str string) bool
func IsISO693Alpha3b(str string) bool
func IsIn(str string, params ...string) bool
func IsInRaw(str string, params ...string) bool
func IsInt(str string) bool
func IsJSON(str string) bool
func IsLatitude(str string) bool
func IsLongitude(str string) bool
func IsLowerCase(str string) bool
func IsMAC(str string) bool
func IsMD4(str string) bool
func IsMD5(str string) bool
func IsMagnetURI(str string) bool
func IsMongoID(str string) bool
func IsMultibyte(str string) bool
func IsNatural(value float64) bool
func IsNegative(value float64) bool
func IsNonNegative(value float64) bool
func IsNonPositive(value float64) bool
func IsNotNull(str string) bool
func IsNull(str string) bool
func IsNumeric(str string) bool
func IsPort(str string) bool
func IsPositive(value float64) bool
func IsPrintableASCII(str string) bool
func IsRFC3339(str string) bool
func IsRFC3339WithoutZone(str string) bool
func IsRGBcolor(str string) bool
func IsRegex(str string) bool
func IsRequestURI(rawurl string) bool
func IsRequestURL(rawurl string) bool
func IsRipeMD128(str string) bool
func IsRipeMD160(str string) bool
func IsRsaPub(str string, params ...string) bool
func IsRsaPublicKey(str string, keylen int) bool
func IsSHA1(str string) bool
func IsSHA256(str string) bool
func IsSHA384(str string) bool
func IsSHA512(str string) bool
func IsSSN(str string) bool
func IsSemver(str string) bool
func IsTiger128(str string) bool
func IsTiger160(str string) bool
func IsTiger192(str string) bool
func IsTime(str string, format string) bool
func IsType(v interface{}, params ...string) bool
func IsURL(str string) bool
func IsUTFDigit(str string) bool
func IsUTFLetter(str string) bool
func IsUTFLetterNumeric(str string) bool
func IsUTFNumeric(str string) bool
func IsUUID(str string) bool
func IsUUIDv3(str string) bool
func IsUUIDv4(str string) bool
func IsUUIDv5(str string) bool
func IsULID(str string) bool
func IsUnixTime(str string) bool
func IsUpperCase(str string) bool
func IsVariableWidth(str string) bool
func IsWhole(value float64) bool
func LeftTrim(str, chars string) string
func Map(array []interface{}, iterator ResultIterator) []interface{}
func Matches(str, pattern string) bool
func MaxStringLength(str string, params ...string) bool
func MinStringLength(str string, params ...string) bool
func NormalizeEmail(str string) (string, error)
func PadBoth(str string, padStr string, padLen int) string
func PadLeft(str string, padStr string, padLen int) string
func PadRight(str string, padStr string, padLen int) string
func PrependPathToErrors(err error, path string) error
func Range(str string, params ...string) bool
func RemoveTags(s string) string
func ReplacePattern(str, pattern, replace string) string
func Reverse(s string) string
func RightTrim(str, chars string) string
func RuneLength(str string, params ...string) bool
func SafeFileName(str string) string
func SetFieldsRequiredByDefault(value bool)
func SetNilPtrAllowedByRequired(value bool)
func Sign(value float64) float64
func StringLength(str string, params ...string) bool
func StringMatches(s string, params ...string) bool
func StripLow(str string, keepNewLines bool) string
func ToBoolean(str string) (bool, error)
func ToFloat(str string) (float64, error)
func ToInt(value interface{}) (res int64, err error)
func ToJSON(obj interface{}) (string, error)
func ToString(obj interface{}) string
func Trim(str, chars string) string
func Truncate(str string, length int, ending string) string
func TruncatingErrorf(str string, args ...interface{}) error
func UnderscoreToCamelCase(s string) string
func ValidateMap(inputMap map[string]interface{}, validationMap map[string]interface{}) (bool, error)
func ValidateStruct(s interface{}) (bool, error)
func WhiteList(str, chars string) string
type ConditionIterator
type CustomTypeValidator
type Error
func (e Error) Error() string
type Errors
func (es Errors) Error() string
func (es Errors) Errors() []error
type ISO3166Entry
type ISO693Entry
type InterfaceParamValidator
type Iterator
type ParamValidator
type ResultIterator
type UnsupportedTypeError
func (e *UnsupportedTypeError) Error() string
type Validator
println(govalidator.IsType("Bob", "string"))
println(govalidator.IsType(1, "int"))
i := 1
println(govalidator.IsType(&i, "*int"))

IsType can be used through the tag type which is essential for map validation:

type User   struct {
  Name string      `valid:"type(string)"`
  Age  int         `valid:"type(int)"`
  Meta interface{} `valid:"type(string)"`
result, err := govalidator.ValidateStruct(User{"Bob", 20, "meta"})
if err != nil {
    println("error: " + err.Error())
type User struct {
    FirstName string
    LastName string

str := govalidator.ToString(&User{"John", "Juan"})
Each, Map, Filter, Count for slices

Each iterates over the slice/array and calls Iterator for every item

data := []interface{}{1, 2, 3, 4, 5}
var fn govalidator.Iterator = func(value interface{}, index int) {
govalidator.Each(data, fn)
data := []interface{}{1, 2, 3, 4, 5}
var fn govalidator.ResultIterator = func(value interface{}, index int) interface{} {
    return value.(int) * 3
_ = govalidator.Map(data, fn) // result = []interface{}{1, 6, 9, 12, 15}
data := []interface{}{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
var fn govalidator.ConditionIterator = func(value interface{}, index int) bool {
    return value.(int)%2 == 0
_ = govalidator.Filter(data, fn) // result = []interface{}{2, 4, 6, 8, 10}
_ = govalidator.Count(data, fn) // result = 5
ValidateStruct #2

If you want to validate structs, you can use tag valid for any field in your structure. All validators used with this field in one tag are separated by comma. If you want to skip validation, place - in your tag. If you need a validator that is not on the list below, you can add it like this:

govalidator.TagMap["duck"] = govalidator.Validator(func(str string) bool {
    return str == "duck"

For completely custom validators (interface-based), see below.

Here is a list of available validators for struct fields (validator - used function):

"email":              IsEmail,
"url":                IsURL,
"dialstring":         IsDialString,
"requrl":             IsRequestURL,
"requri":             IsRequestURI,
"alpha":              IsAlpha,
"utfletter":          IsUTFLetter,
"alphanum":           IsAlphanumeric,
"utfletternum":       IsUTFLetterNumeric,
"numeric":            IsNumeric,
"utfnumeric":         IsUTFNumeric,
"utfdigit":           IsUTFDigit,
"hexadecimal":        IsHexadecimal,
"hexcolor":           IsHexcolor,
"rgbcolor":           IsRGBcolor,
"lowercase":          IsLowerCase,
"uppercase":          IsUpperCase,
"int":                IsInt,
"float":              IsFloat,
"null":               IsNull,
"uuid":               IsUUID,
"uuidv3":             IsUUIDv3,
"uuidv4":             IsUUIDv4,
"uuidv5":             IsUUIDv5,
"creditcard":         IsCreditCard,
"isbn10":             IsISBN10,
"isbn13":             IsISBN13,
"json":               IsJSON,
"multibyte":          IsMultibyte,
"ascii":              IsASCII,
"printableascii":     IsPrintableASCII,
"fullwidth":          IsFullWidth,
"halfwidth":          IsHalfWidth,
"variablewidth":      IsVariableWidth,
"base64":             IsBase64,
"datauri":            IsDataURI,
"ip":                 IsIP,
"port":               IsPort,
"ipv4":               IsIPv4,
"ipv6":               IsIPv6,
"dns":                IsDNSName,
"host":               IsHost,
"mac":                IsMAC,
"latitude":           IsLatitude,
"longitude":          IsLongitude,
"ssn":                IsSSN,
"semver":             IsSemver,
"rfc3339":            IsRFC3339,
"rfc3339WithoutZone": IsRFC3339WithoutZone,
"ISO3166Alpha2":      IsISO3166Alpha2,
"ISO3166Alpha3":      IsISO3166Alpha3,
"ulid":               IsULID,

Validators with parameters

"range(min|max)": Range,
"length(min|max)": ByteLength,
"runelength(min|max)": RuneLength,
"stringlength(min|max)": StringLength,
"matches(pattern)": StringMatches,
"in(string1|string2|...|stringN)": IsIn,
"rsapub(keylength)" : IsRsaPub,
"minstringlength(int): MinStringLength,
"maxstringlength(int): MaxStringLength,

Validators with parameters for any type

"type(type)": IsType,

And here is small example of usage:

type Post struct {
    Title    string `valid:"alphanum,required"`
    Message  string `valid:"duck,ascii"`
    Message2 string `valid:"animal(dog)"`
    AuthorIP string `valid:"ipv4"`
    Date     string `valid:"-"`
post := &Post{
    Title:   "My Example Post",
    Message: "duck",
    Message2: "dog",
    AuthorIP: "",

// Add your own struct validation tags
govalidator.TagMap["duck"] = govalidator.Validator(func(str string) bool {
    return str == "duck"

// Add your own struct validation tags with parameter
govalidator.ParamTagMap["animal"] = govalidator.ParamValidator(func(str string, params ...string) bool {
    species := params[0]
    return str == species
govalidator.ParamTagRegexMap["animal"] = regexp.MustCompile("^animal\\((\\w+)\\)$")

result, err := govalidator.ValidateStruct(post)
if err != nil {
    println("error: " + err.Error())
ValidateMap #2

If you want to validate maps, you can use the map to be validated and a validation map that contain the same tags used in ValidateStruct, both maps have to be in the form map[string]interface{}

So here is small example of usage:

var mapTemplate = map[string]interface{}{

var inputMap = map[string]interface{}{
    "email":"[email protected]",

result, err := govalidator.ValidateMap(inputMap, mapTemplate)
if err != nil {
    println("error: " + err.Error())
// Remove all characters from string ignoring characters between "a" and "z"
println(govalidator.WhiteList("a3a43a5a4a3a2a23a4a5a4a3a4", "a-z") == "aaaaaaaaaaaa")
Custom validation functions

Custom validation using your own domain specific validators is also available - here's an example of how to use it:

import "github.com/asaskevich/govalidator"

type CustomByteArray [6]byte // custom types are supported and can be validated

type StructWithCustomByteArray struct {
  ID              CustomByteArray `valid:"customByteArrayValidator,customMinLengthValidator"` // multiple custom validators are possible as well and will be evaluated in sequence
  Email           string          `valid:"email"`
  CustomMinLength int             `valid:"-"`

govalidator.CustomTypeTagMap.Set("customByteArrayValidator", func(i interface{}, context interface{}) bool {
  switch v := context.(type) { // you can type switch on the context interface being validated
  case StructWithCustomByteArray:
    // you can check and validate against some other field in the context,
    // return early or not validate against the context at all – your choice
  case SomeOtherType:
    // ...
    // expecting some other type? Throw/panic here or continue

  switch v := i.(type) { // type switch on the struct field being validated
  case CustomByteArray:
    for _, e := range v { // this validator checks that the byte array is not empty, i.e. not all zeroes
      if e != 0 {
        return true
  return false
govalidator.CustomTypeTagMap.Set("customMinLengthValidator", func(i interface{}, context interface{}) bool {
  switch v := context.(type) { // this validates a field against the value in another field, i.e. dependent validation
  case StructWithCustomByteArray:
    return len(v.ID) >= v.CustomMinLength
  return false
Loop over Error()

By default .Error() returns all errors in a single String. To access each error you can do this:

  if err != nil {
    errs := err.(govalidator.Errors).Errors()
    for _, e := range errs {
Custom error messages

Custom error messages are supported via annotations by adding the ~ separator - here's an example of how to use it:

type Ticket struct {
  Id        int64     `json:"id"`
  FirstName string    `json:"firstname" valid:"required~First name is blank"`

Documentation is available here: godoc.org. Full information about code coverage is also available here: govalidator on gocover.io.


If you do have a contribution to the package, feel free to create a Pull Request or an Issue.

What to contribute

If you don't know what to do, there are some features and functions that need to be done

  • [ ] Refactor code
  • [ ] Edit docs and README: spellcheck, grammar and typo check
  • [ ] Create actual list of contributors and projects that currently using this package
  • [ ] Resolve issues and bugs
  • [ ] Update actual list of functions
  • [ ] Update list of validators that available for ValidateStruct and add new
  • [ ] Implement new validators: IsFQDN, IsIMEI, IsPostalCode, IsISIN, IsISRC etc
  • [x] Implement validation by maps
  • [ ] Implement fuzzing testing
  • [ ] Implement some struct/map/array utilities
  • [ ] Implement map/array validation
  • [ ] Implement benchmarking
  • [ ] Implement batch of examples
  • [ ] Look at forks for new features and fixes

Feel free to create what you want, but keep in mind when you implement new features:

  • Code must be clear and readable, names of variables/constants clearly describes what they are doing
  • Public functions must be documented and described in source file and added to README.md to the list of available functions
  • There are must be unit-tests for any new functions and improvements



This project exists thanks to all the people who contribute. [[Contribute](CONTRIBUTING.md)].

Special thanks to contributors


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FOSSA Status

*Note that all licence references and agreements mentioned in the govalidator README section above are relevant to that project's source code only.