Go Validator Validator Save

Package validator implements struct field validations

Project README

Package validator

Package validator implements variable validations


Just use go get.

go get gopkg.in/validator.v2

And then just import the package into your own code.

import (


Please see http://godoc.org/gopkg.in/validator.v2 for detailed usage docs. A simple example would be.

type NewUserRequest struct {
	Username string `validate:"min=3,max=40,regexp=^[a-zA-Z]*$"`
	Name string     `validate:"nonzero"`
	Age int         `validate:"min=21"`
	Password string `validate:"min=8"`

nur := NewUserRequest{Username: "something", Age: 20}
if errs := validator.Validate(nur); errs != nil {
	// values not valid, deal with errors here

Builtin validators

Here is the list of validators buildin in the package. Validators buildin will check the element pointed to if the value to check is a pointer. The nil pointer is treated as a valid value by validators buildin other than nonzero, so you should to use nonzero if you don't want to accept a nil pointer.

	For numeric numbers, len will simply make sure that the
	value is equal to the parameter given. For strings, it
	checks that the string length is exactly that number of
	characters. For slices,	arrays, and maps, validates the
	number of items. (Usage: len=10)

	For numeric numbers, max will simply make sure that the
	value is lesser or equal to the parameter given. For strings,
	it checks that the string length is at most that number of
	characters. For slices,	arrays, and maps, validates the
	number of items. (Usage: max=10)

	For numeric numbers, min will simply make sure that the value
	is greater or equal to the parameter given. For strings, it
	checks that the string length is at least that number of
	characters. For slices, arrays, and maps, validates the
	number of items. (Usage: min=10)

	This validates that the value is not zero. The appropriate
	zero value is given by the Go spec (e.g. for int it's 0, for
	string it's "", for pointers is nil, etc.) For structs, it
	will not check to see if the struct itself has all zero
	values, instead use a pointer or put nonzero on the struct's
	keys that you care about. For pointers, the pointer's value
	is used to test for nonzero in addition to the pointer itself
	not being nil. To just check for not being nil, use `nonnil`.
	(Usage: nonzero)

	Only valid for string types, it will validate that the
	value matches the regular expression provided as parameter.
	Commas need to be escaped with 2 backslashes `\\`.
	(Usage: regexp=^a.*b$)

	Validates that the given value is not nil. (Usage: nonnil)

Custom validators

It is possible to define custom validators by using SetValidationFunc. First, one needs to create a validation function.

// Very simple validator
func notZZ(v interface{}, param string) error {
	st := reflect.ValueOf(v)
	if st.Kind() != reflect.String {
		return errors.New("notZZ only validates strings")
	if st.String() == "ZZ" {
		return errors.New("value cannot be ZZ")
	return nil

Then one needs to add it to the list of validators and give it a "tag" name.

validator.SetValidationFunc("notzz", notZZ)

Then it is possible to use the notzz validation tag. This will print "Field A error: value cannot be ZZ"

type T struct {
	A string  `validate:"nonzero,notzz"`
t := T{"ZZ"}
if errs := validator.Validate(t); errs != nil {
	fmt.Printf("Field A error: %s\n", errs["A"][0])

You can also have multiple sets of validator rules with SetTag().

type T struct {
	A int `foo:"nonzero" bar:"min=10"`
t := T{5}
validator.Validate(t) // valid as it's nonzero
validator.Validate(t) // invalid as it's less than 10

SetTag is probably better used with multiple validators.

fooValidator := validator.NewValidator()
barValidator := validator.NewValidator()

This keeps the default validator's tag clean. Again, please refer to godocs for a lot of more examples and different uses.

Pull requests policy

tl;dr. Contributions are welcome.

The repository is organized in version branches. Pull requests to, say, the v2 branch that break API compatibility will not be accepted. It is okay to break the API in master, not in the branches.

As for validation functions, the preference is to keep the main code simple and add most new functions to the validator-contrib repository.


For improvements and/or fixes to the builtin validation functions, please make sure the behaviour will not break existing functionality in the branches. If you see a case where the functionality of the builtin will change significantly, please send a pull request against master. We can discuss then whether the changes should be incorporated in the version branches as well.


Copyright 2014 Roberto Teixeira [email protected]

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at


Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

Open Source Agenda is not affiliated with "Go Validator Validator" Project. README Source: go-validator/validator
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