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This is a modified version based off to have better i18n support for the binding middleware.

Package validator implements value validations for structs and individual fields based on tags.

It has the following unique features:

  • Cross Field and Cross Struct validations by using validation tags or custom validators.
  • Slice, Array and Map diving, which allows any or all levels of a multidimensional field to be validated.
  • Ability to dive into both map keys and values for validation
  • Handles type interface by determining it’s underlying type prior to validation.
  • Handles custom field types such as sql driver Valuer see Valuer
  • Alias validation tags, which allows for mapping of several validations to a single tag for easier defining of validations on structs
  • Extraction of custom defined Field Name e.g. can specify to extract the JSON name while validating and have it available in the resulting FieldError
  • Customizable i18n aware error messages.


The minimum requirement of Go is 1.16.

go get

Error return value

Validation functions return type error to avoid the issue discussed in the following, where err is always != nil:

Validator returns only InvalidValidationError for bad validation input, nil or ValidationErrors as type error; so, in your code all you need to do is check if the error returned is not nil, and if it’s not check if error is InvalidValidationError ( if necessary, most of the time it isn’t ) type cast it to type ValidationErrors like so:

err := validate.Struct(mystruct)
validationErrors := err.(validator.ValidationErrors)

Usage and documentation

Please see for detailed usage docs.


Baked-in validations


Tag Description
eqcsfield Field Equals Another Field (relative)
eqfield Field Equals Another Field
fieldcontains NOT DOCUMENTED IN doc.go
fieldexcludes NOT DOCUMENTED IN doc.go
gtcsfield Field Greater Than Another Relative Field
gtecsfield Field Greater Than or Equal To Another Relative Field
gtefield Field Greater Than or Equal To Another Field
gtfield Field Greater Than Another Field
ltcsfield Less Than Another Relative Field
ltecsfield Less Than or Equal To Another Relative Field
ltefield Less Than or Equal To Another Field
ltfield Less Than Another Field
necsfield Field Does Not Equal Another Field (relative)
nefield Field Does Not Equal Another Field


Tag Description
cidr Classless Inter-Domain Routing CIDR
cidrv4 Classless Inter-Domain Routing CIDRv4
cidrv6 Classless Inter-Domain Routing CIDRv6
datauri Data URL
fqdn Full Qualified Domain Name (FQDN)
hostname Hostname RFC 952
hostname_port HostPort
hostname_rfc1123 Hostname RFC 1123
ip Internet Protocol Address IP
ip4_addr Internet Protocol Address IPv4
ip6_addr Internet Protocol Address IPv6
ip_addr Internet Protocol Address IP
ipv4 Internet Protocol Address IPv4
ipv6 Internet Protocol Address IPv6
mac Media Access Control Address MAC
tcp4_addr Transmission Control Protocol Address TCPv4
tcp6_addr Transmission Control Protocol Address TCPv6
tcp_addr Transmission Control Protocol Address TCP
udp4_addr User Datagram Protocol Address UDPv4
udp6_addr User Datagram Protocol Address UDPv6
udp_addr User Datagram Protocol Address UDP
unix_addr Unix domain socket end point Address
uri URI String
url URL String
url_encoded URL Encoded
urn_rfc2141 Urn RFC 2141 String


Tag Description
alpha Alpha Only
alphanum Alphanumeric
alphanumunicode Alphanumeric Unicode
alphaunicode Alpha Unicode
ascii ASCII
boolean Boolean
contains Contains
containsany Contains Any
containsrune Contains Rune
endsnotwith Ends With
endswith Ends With
excludes Excludes
excludesall Excludes All
excludesrune Excludes Rune
lowercase Lowercase
multibyte Multi-Byte Characters
number NOT DOCUMENTED IN doc.go
numeric Numeric
printascii Printable ASCII
startsnotwith Starts Not With
startswith Starts With
uppercase Uppercase


Tag Description
base64 Base64 String
base64url Base64URL String
bic Business Identifier Code (ISO 9362)
bcp47_language_tag Language tag (BCP 47)
btc_addr Bitcoin Address
btc_addr_bech32 Bitcoin Bech32 Address (segwit)
datetime Datetime
e164 e164 formatted phone number
email E-mail String
eth_addr Ethereum Address
hexadecimal Hexadecimal String
hexcolor Hexcolor String
hsl HSL String
hsla HSLA String
html HTML Tags
html_encoded HTML Encoded
isbn International Standard Book Number
isbn10 International Standard Book Number 10
isbn13 International Standard Book Number 13
iso3166_1_alpha2 Two-letter country code (ISO 3166-1 alpha-2)
iso3166_1_alpha3 Three-letter country code (ISO 3166-1 alpha-3)
iso3166_1_alpha_numeric Numeric country code (ISO 3166-1 numeric)
iso3166_2 Country subdivision code (ISO 3166-2)
iso4217 Currency code (ISO 4217)
json JSON
jwt JSON Web Token (JWT)
latitude Latitude
longitude Longitude
postcode_iso3166_alpha2 Postcode
postcode_iso3166_alpha2_field Postcode
rgb RGB String
rgba RGBA String
ssn Social Security Number SSN
timezone Timezone
uuid Universally Unique Identifier UUID
uuid3 Universally Unique Identifier UUID v3
uuid3_rfc4122 Universally Unique Identifier UUID v3 RFC4122
uuid4 Universally Unique Identifier UUID v4
uuid4_rfc4122 Universally Unique Identifier UUID v4 RFC4122
uuid5 Universally Unique Identifier UUID v5
uuid5_rfc4122 Universally Unique Identifier UUID v5 RFC4122
uuid_rfc4122 Universally Unique Identifier UUID RFC4122


Tag Description
eq Equals
gt Greater than
gte Greater than or equal
lt Less Than
lte Less Than or Equal
ne Not Equal


Tag Description
dir Directory
file File path
isdefault Is Default
len Length
max Maximum
min Minimum
oneof One Of
required Required
required_if Required If
required_unless Required Unless
required_with Required With
required_with_all Required With All
required_without Required Without
required_without_all Required Without All
excluded_with Excluded With
excluded_with_all Excluded With All
excluded_without Excluded Without
excluded_without_all Excluded Without All
unique Unique


Tag Description
iscolor hexcolor|rgb|rgba|hsl|hsla
country_code iso3166_1_alpha2|iso3166_1_alpha3|iso3166_1_alpha_numeric


This project is under the MIT License. See the LICENSE file for the full license text.