go-validatex

Struct validation library for Go using struct tags. Zero external dependencies

Installation

go get github.com/philiprehberger/go-validatex

Usage

package main

import (
	"fmt"
	"github.com/philiprehberger/go-validatex"
)

type User struct {
	Name  string `validate:"required,min=3,max=50"`
	Email string `validate:"required,email"`
	Role  string `validate:"oneof=admin|user|guest"`
	Age   int    `validate:"min=18,max=120"`
}

func main() {
	u := User{Name: "Al", Email: "bad", Role: "superadmin", Age: 10}
	err := validatex.Validate(u)
	if err != nil {
		for _, ve := range validatex.Errors(err) {
			fmt.Printf("Field %s (%s): %s\n", ve.Field, ve.Rule, ve.Message)
		}
	}
}

Custom Messages

Use the msg tag option to provide a custom error message for the preceding rule:

type User struct {
	Name  string `validate:"required,msg=Name is required"`
	Email string `validate:"email,msg=Please enter a valid email"`
}

Nested Structs

Nested structs with validate tags are validated automatically. Error field paths use dot notation:

type Address struct {
	Street string `validate:"required"`
	City   string `validate:"required"`
}

type User struct {
	Name    string  `validate:"required"`
	Address Address
}

err := validatex.Validate(User{Name: "Alice", Address: Address{}})
// errors: Address.Street: is required, Address.City: is required

ValidateField

Validate a single value against a rules string without defining a struct:

err := validatex.ValidateField("bad", "email")
err = validatex.ValidateField("", "required,min=3")
err = validatex.ValidateField(42, "min=10,max=100")

Custom Rules

validatex.Register("even", func(value any, param string) error {
	v, ok := value.(int)
	if !ok {
		return fmt.Errorf("expected int")
	}
	if v%2 != 0 {
		return fmt.Errorf("must be even")
	}
	return nil
})

type Config struct {
	Workers int `validate:"even,min=2"`
}

Built-in Rules

Rule	Applies To	Description
required	string, int, float	Non-empty string or non-zero number
min=N	string, int, float	Min length (string) or min value (number)
max=N	string, int, float	Max length (string) or max value (number)
len=N	string	Exact length
email	string	Must contain @ and .
url	string	Must start with http:// or https://
oneof=a|b|c	string	Must be one of the listed values
pattern=regex	string	Must match the regular expression
uuid	string	Must be a valid UUID (8-4-4-4-12 hex format)
ip	string	Must be a valid IPv4 or IPv6 address
ipv4	string	Must be a valid IPv4 address
ipv6	string	Must be a valid IPv6 address
alpha	string	Must contain only ASCII letters
numeric	string	Must contain only ASCII digits
alphanum	string	Must contain only ASCII letters and digits
contains=X	string	Must contain substring X
excludes=X	string	Must not contain substring X

API

Function / Type	Description
Validate(v any) error	Validate struct fields using validate tags (supports nested structs)
ValidateField(value any, rules string) error	Validate a single value against a rules string
Register(name, fn)	Register a custom validation rule
Errors(err) []ValidationError	Extract individual errors from a validation error
ValidationError	Single field validation failure (Field, Rule, Message)
ValidationErrors	Slice of ValidationError, implements error

Development

go test ./...
go vet ./...

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License

MIT