Data Validation in Go: Overview of Libraries and Approaches

Data Validation in Go (Golang): Libraries and Practical Examples

Data validation is one of the key aspects of developing reliable web applications and APIs in Go. Without proper validation of incoming data, an application becomes vulnerable to errors, incorrect input, and attacks. In this article, we will look at three popular libraries for validation in Go: go-playground/validator, ozzo-validation, and govalidator, and also analyze examples of their use.

Why is validation needed in Go?

Go is a strongly typed language, but this does not protect against logical errors in data: empty strings, invalid emails, numbers outside an acceptable range. Validation allows you to:

• Guarantee data integrity at the input;
• Simplify error handling;
• Increase application security;
• Reduce the amount of boilerplate code.

1. go-playground/validator — The Gold Standard

The most popular library (over 15k stars on GitHub). It allows you to describe validation rules directly in struct tags.

Installation

go get github.com/go-playground/validator/v10

Basic Example

package main

import (    "fmt"    "github.com/go-playground/validator/v10")

type User struct {    Name  string `validate:"required,min=3,max=50"`    Email string `validate:"required,email"`    Age   int    `validate:"gte=18,lte=120"`}

func main() {    validate := validator.New()    user := User{        Name:  "A",        Email: "invalid-email",        Age:   15,    }    err := validate.Struct(user)    if err != nil {        for _, err := range err.(validator.ValidationErrors) {            fmt.Printf("Field: %s, Error: %s", err.Field(), err.Tag())        }    }}

Custom Validators

validate.RegisterValidation("is-valid-username", func(fl validator.FieldLevel) bool {    return len(fl.Field().String()) >= 5})

type Login struct {    Username string `validate:"required,is-valid-username"`}

2. ozzo-validation — Flexibility and Readability

The ozzo-validation library offers a fluent interface for building rules. It is well suited for complex business rules.

Installation

go get github.com/go-ozzo/ozzo-validation/v4

Usage Example

package main

import (    "fmt"    validation "github.com/go-ozzo/ozzo-validation/v4"    "github.com/go-ozzo/ozzo-validation/v4/is")

type Order struct {    ProductID string    Quantity  int    Email     string}

func (o Order) Validate() error {    return validation.ValidateStruct(&o,        validation.Field(&o.ProductID, validation.Required, validation.Length(5, 20)),        validation.Field(&o.Quantity, validation.Required, validation.Min(1), validation.Max(100)),        validation.Field(&o.Email, validation.Required, is.Email),    )}

func main() {    order := Order{ProductID: "AB", Quantity: 0, Email: "bad"}    err := order.Validate()    if err != nil {        fmt.Println(err)    }}

Features

• No tags — rules are written in code;
• Easy integration with custom types;
• Support for conditional validation.

3. govalidator — Simplicity for Small Projects

A lightweight library with a set of ready-made functions for validating strings, numbers, and structs.

Installation

go get github.com/asaskevich/govalidator

Example

package main

import (    "fmt"    "github.com/asaskevich/govalidator")

func main() {    // String validation    fmt.Println(govalidator.IsEmail("test@example.com"))       // true    fmt.Println(govalidator.IsURL("https://pythonlib.ru"))     // true    fmt.Println(govalid