✅ GoValidate — Struct Validation for Go

Tag-based validation with 20+ built-in rules, nested struct support, and custom rules — zero dependencies.

GoValidate provides declarative struct validation using Go struct tags. Supports nested structs, slices, custom rules, and JSON field names — all with zero external dependencies.

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📦 Features

Feature	Description
Struct Tags	validate:"required,min=3,max=100"
20+ Built-in Rules	required, min, max, email, url, ip, alpha, regex...
Nested Structs	Recursive validation with dot-notation errors
Slice Validation	Validates each element: Items[0].Name
Custom Rules	RegisterRule("phone", fn)
JSON Names	Uses json tag name in error messages
Error Map	errs.Map() → map[string][]string
Cross-field	oneof, numeric comparisons
Zero Dependencies	Only Go standard library + reflect

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🚀 Quick Start

go get github.com/kzxl/govalidate

package main
import (
"fmt""github.com/kzxl/govalidate"
)
typeUserstruct {
Namestring`json:"name" validate:"required,min=3,max=50"`Emailstring`json:"email" validate:"required,email"`Ageint`json:"age" validate:"gte=0,lte=150"`Passwordstring`json:"password" validate:"required,min=8"`Rolestring`json:"role" validate:"oneof=admin user moderator"`
}
funcmain() {
user:=User{
Name: "Jo", // too shortEmail: "invalid", // bad emailAge: -1, // negative
}
errs:=govalidate.Validate(user)
iferrs.HasErrors() {
for_, e:=rangeerrs.Errors {
fmt.Printf(" %s [%s]: %s\n", e.Field, e.Rule, e.Message)
}
// Output:// name [min]: must be at least 3 characters// email [email]: must be a valid email address// age [gte]: must be >= 0// password [required]: is required
}
// Error map for API responsesfmt.Println(errs.Map())
// map[name:[must be at least 3 characters] email:[must be a valid email] ...]
}

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📖 Built-in Rules

Rule	Example	Description
required	validate:"required"	Field must not be zero value
min	validate:"min=3"	Min length (string/slice) or min value (number)
max	validate:"max=100"	Max length or value
len	validate:"len=5"	Exact length
gt / gte	validate:"gt=0"	Greater than / greater than or equal
lt / lte	validate:"lte=100"	Less than / less than or equal
email	validate:"email"	Valid email format
url	validate:"url"	Valid URL with scheme and host
ip	validate:"ip"	Valid IPv4 or IPv6
alpha	validate:"alpha"	Letters only
alphanum	validate:"alphanum"	Letters and numbers only
numeric	validate:"numeric"	Numeric characters only
lowercase	validate:"lowercase"	Must be all lowercase
uppercase	validate:"uppercase"	Must be all uppercase
contains	validate:"contains=keyword"	Must contain substring
startswith	validate:"startswith=Hello"	Must start with prefix
endswith	validate:"endswith=!"	Must end with suffix
oneof	validate:"oneof=admin user"	Must be one of listed values
regex	validate:"regex=^\\d{3}$"	Must match regex pattern
datetime	validate:"datetime=2006-01-02"	Must parse with Go layout

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🔧 Custom Rules

govalidate.RegisterRule("phone", func(v reflect.Value, paramstring) string {
ifv.Kind() !=reflect.String { return"" }
if!phoneRegex.MatchString(v.String()) {
return"must be a valid phone number"
}
return""
})
typeContactstruct {
Phonestring`validate:"required,phone"`
}

---

🏗️ Nested Struct & Slice Validation

typeOrderstruct {
CustomerCustomer`validate:"required"`Items []Item`validate:"min=1"`
}
typeItemstruct {
Namestring`validate:"required"`Priceint`validate:"gt=0"`
}
// Errors:// customer.name: is required// Items[0].Price: must be > 0

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📄 License

Apache License 2.0 — See LICENSE for details.

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✅ Validate structs, the Go way.