Part 2: Complete Validation Reference

This section provides comprehensive reference tables for all available validation rules in validator/v10.

String Validation Rules {#ref-strings}

Format Validations

Rule	Description	Example	Valid Values
`email`	Valid email address	`validate:"email"`	`user@example.com`
`url`	Valid URL (must have scheme)	`validate:"url"`	`https://example.com`
`uri`	Valid URI (can be relative)	`validate:"uri"`	`/api/users`
`alpha`	Letters only (A-Z, a-z)	`validate:"alpha"`	`JohnDoe`
`alphanum`	Letters and numbers	`validate:"alphanum"`	`user123`
`alphaunicode`	Letters with unicode	`validate:"alphaunicode"`	`José`
`ascii`	ASCII characters only	`validate:"ascii"`	`Hello123`
`lowercase`	All lowercase	`validate:"lowercase"`	`hello`
`uppercase`	All uppercase	`validate:"uppercase"`	`HELLO`
`hexcolor`	Hex color code	`validate:"hexcolor"`	`#FF5733`, `#F00`
`uuid`	UUID (any version)	`validate:"uuid"`	`550e8400-e29b-41d4-a716-446655440000`
`uuid3`	UUID version 3	`validate:"uuid3"`	UUID v3 format
`uuid4`	UUID version 4	`validate:"uuid4"`	UUID v4 format
`uuid5`	UUID version 5	`validate:"uuid5"`	UUID v5 format
`ulid`	ULID format	`validate:"ulid"`	`01ARZ3NDEKTSV4RRFFQ69G5FAV`
`ip`	IP address (v4 or v6)	`validate:"ip"`	`192.168.1.1`, `2001:db8::8a2e:370:7334`
`ipv4`	IPv4 address	`validate:"ipv4"`	`192.168.1.1`
`ipv6`	IPv6 address	`validate:"ipv6"`	`2001:db8::8a2e:370:7334`
`mac`	MAC address	`validate:"mac"`	`01:23:45:67:89:ab`
`json`	Valid JSON string	`validate:"json"`	`{"key":"value"}`
`base64`	Base64 encoded	`validate:"base64"`	`SGVsbG8=`
`jwt`	JWT token	`validate:"jwt"`	`eyJhbGc...`
`e164`	E.164 phone format	`validate:"e164"`	`+12345678901`
`isbn`	ISBN-10 or ISBN-13	`validate:"isbn"`	`978-3-16-148410-0`
`isbn10`	ISBN-10	`validate:"isbn10"`	`0-306-40615-2`
`isbn13`	ISBN-13	`validate:"isbn13"`	`978-0-306-40615-7`

Length Validations

Rule	Description	Example	Notes
`min`	Minimum length	`validate:"min=5"`	Min 5 characters
`max`	Maximum length	`validate:"max=20"`	Max 20 characters
`len`	Exact length	`validate:"len=10"`	Exactly 10 characters
`eq`	Equal to value	`validate:"eq=admin"`	Must be “admin”
`ne`	Not equal to value	`validate:"ne=banned"`	Cannot be “banned”

Pattern Matching

Rule	Description	Example	Notes
`contains`	Contains substring	`validate:"contains=Go"`	Must contain “Go”
`excludes`	Doesn’t contain substring	`validate:"excludes=<script>"`	Cannot contain "
`startswith`	Starts with string	`validate:"startswith=blog-"`	Must start with “blog-”
`endswith`	Ends with string	`validate:"endswith=.jpg"`	Must end with “.jpg”
`regex`	Matches regex pattern	`validate:"regex=^[a-z]+$"`	Custom regex pattern

Number Validation Rules {#ref-numbers}

Comparison Validations

Rule	Description	Example	Notes
`eq`	Equal to	`validate:"eq=5"`	Must equal 5
`ne`	Not equal to	`validate:"ne=0"`	Cannot be 0
`gt`	Greater than	`validate:"gt=0"`	Must be > 0
`gte`	Greater than or equal	`validate:"gte=18"`	Must be >= 18
`lt`	Less than	`validate:"lt=100"`	Must be < 100
`lte`	Less than or equal	`validate:"lte=120"`	Must be <= 120
`min`	Minimum value	`validate:"min=1"`	Min value 1
`max`	Maximum value	`validate:"max=100"`	Max value 100

Numeric Type Validations

Rule	Description	Example	Notes
`numeric`	Numeric value (as string)	`validate:"numeric"`	”123”, “123.45”
`number`	Is a number	`validate:"number"`	Integer or float
`integer`	Integer value	`validate:"integer"`	Whole numbers only
`decimal`	Decimal number	`validate:"decimal"`	Has decimal point

Special Number Validations

Rule	Description	Example	Notes
`multipleOf`	Multiple of value	`validate:"multipleOf=5"`	5, 10, 15, 20…
`oneof`	One of specific values	`validate:"oneof=1 2 3 4 5"`	Enum for numbers

Array/Slice Validation Rules {#ref-arrays}

Rule	Description	Example	Notes
`min`	Minimum array length	`validate:"min=1"`	At least 1 element
`max`	Maximum array length	`validate:"max=5"`	At most 5 elements
`len`	Exact array length	`validate:"len=3"`	Exactly 3 elements
`unique`	All elements unique	`validate:"unique"`	No duplicates
`dive`	Validate each element	`validate:"dive,email"`	Each element must be valid email
`dive,keys,dive`	Validate map keys	`validate:"dive,keys,dive,email"`	For map validations

Date/Time Validation Rules {#ref-dates}

Rule	Description	Example	Notes
`datetime`	Date in specific format	`validate:"datetime=2006-01-02"`	Go time format
`timezone`	Valid timezone	Custom rule	America/New_York

Date Comparison (Cross-Field)

Rule	Description	Example	Notes
`gtefield`	Greater than or equal to field	`validate:"gtefield=StartDate"`	EndDate >= StartDate
`gtfield`	Greater than field	`validate:"gtfield=StartDate"`	EndDate > StartDate
`ltefield`	Less than or equal to field	`validate:"ltefield=EndDate"`	StartDate <= EndDate
`ltfield`	Less than field	`validate:"ltfield=EndDate"`	StartDate < EndDate

Boolean Validation Rules {#ref-booleans}

Rule	Description	Example	Notes
`boolean`	Is a boolean	`validate:"boolean"`	true or false
`eq`	Must equal value	`validate:"eq=true"`	Must be true
`ne`	Must not equal value	`validate:"ne=true"`	Must be false

File Validation Rules {#ref-files}

Rule	Description	Example	Notes
`file`	Valid file path	`validate:"file"`	File exists
`filepath`	Valid file path format	`validate:"filepath"`	Path format only
`dirpath`	Valid directory path	`validate:"dirpath"`	Directory format
`endswith`	File extension check	`validate:"endswith=.jpg"`	Check extension

Database Validation Rules {#ref-database}

Rule	Description	Example	Notes
`iso3166_1_alpha2`	ISO 3166-1 alpha-2 country code	`validate:"iso3166_1_alpha2"`	US, CA, GB, etc.
`iso3166_1_alpha3`	ISO 3166-1 alpha-3 country code	`validate:"iso3166_1_alpha3"`	USA, CAN, GBR, etc.
`iso4217`	ISO 4217 currency code	`validate:"iso4217"`	USD, EUR, GBP, etc.

Utility Validation Rules {#ref-utilities}

Required/Optional Rules

Rule	Description	Example	Notes
`required`	Field must have value	`validate:"required"`	Cannot be empty/zero
`required_if`	Required if condition	`validate:"required_if=Field value"`	Conditional required
`required_unless`	Required unless condition	`validate:"required_unless=Field value"`	Inverse conditional
`required_with`	Required with another field	`validate:"required_with=Field"`	Both or neither
`required_with_all`	Required with all fields	`validate:"required_with_all=F1 F2"`	All or none
`required_without`	Required without another	`validate:"required_without=Field"`	One must exist
`required_without_all`	Required without all	`validate:"required_without_all=F1 F2"`	At least one required
`omitempty`	Skip validation if empty	`validate:"omitempty,email"`	Validate only if present
`omitnil`	Skip validation if nil	`validate:"omitnil"`	For pointers

Exclusion Rules

Rule	Description	Example	Notes
`excluded_if`	Excluded if condition	`validate:"excluded_if=Type business"`	Must be empty when condition met
`excluded_unless`	Excluded unless condition	`validate:"excluded_unless=Active true"`	Must be empty unless condition
`excluded_with`	Excluded with another field	`validate:"excluded_with=Field"`	Cannot coexist
`excluded_without`	Excluded without another	`validate:"excluded_without=Field"`	Requires other field

Cross-Field Comparisons

Rule	Description	Example	Notes
`eqfield`	Equal to another field	`validate:"eqfield=Password"`	Field matching
`nefield`	Not equal to another field	`validate:"nefield=OldEmail"`	Must be different
`gtfield`	Greater than another field	`validate:"gtfield=MinPrice"`	Range validation
`gtefield`	Greater than or equal field	`validate:"gtefield=MinAge"`	Range validation
`ltfield`	Less than another field	`validate:"ltfield=MaxPrice"`	Range validation
`ltefield`	Less than or equal field	`validate:"ltefield=MaxAge"`	Range validation
`eqcsfield`	Equal (cross-struct)	`validate:"eqcsfield=Struct.Field"`	Cross-struct comparison
`necsfield`	Not equal (cross-struct)	`validate:"necsfield=Struct.Field"`	Cross-struct comparison

Special Rules

Rule	Description	Example	Notes
`oneof`	One of enumerated values	`validate:"oneof=red blue green"`	Enum validation
`-`	Skip field	`validate:"-"`	Ignore this field

Common Validation Patterns

Password Validation


Password string `validate:"required,min=8,max=72"`
// Or with custom strong password rule
Password string `validate:"required,strong_password"`

Email & Username


Email    string `validate:"required,email"`
Username string `validate:"required,min=3,max=20,alphanum"`

URL & Slug


Website string `validate:"omitempty,url"`
Slug    string `validate:"required,lowercase,alphanum"`

Phone & Address


Phone   string `validate:"required,e164"`
ZIPCode string `validate:"required,len=5,numeric"`
Country string `validate:"required,iso3166_1_alpha2"` // US, CA, UK

Numbers & Ranges


Age      int     `validate:"required,gte=18,lte=120"`
Price    float64 `validate:"required,gt=0"`
Quantity int     `validate:"required,min=1,multipleOf=5"`

Arrays


Tags   []string `validate:"required,min=1,max=5,dive,alpha"`
Emails []string `validate:"required,dive,email"`
IDs    []int    `validate:"required,unique,dive,gt=0"`

Dates


BirthDate time.Time `validate:"required"`
EventDate time.Time `validate:"required,gtefield=BirthDate"`

Conditional


ShipDifferent bool   `validate:"boolean"`
ShipAddress   string `validate:"required_if=ShipDifferent true"`

Cross-Field


Password        string `validate:"required,min=8"`
ConfirmPassword string `validate:"required,eqfield=Password"`

Validation Tag Operators

Operator	Description	Example
`,`	AND (all must pass)	`validate:"required,email,max=100"`
`	`	OR (at least one must pass)

Best Practices for Validation Rules

Always use omitempty for optional fields


Bio string `validate:"omitempty,min=10,max=500"`

Use pointers for nullable fields
```
Age *int `validate:"omitempty,gte=0"`
```

Combine validations logically


Email string `validate:"required,email,max=255"`

Use custom validations for business rules


Username string `validate:"required,username"` // Custom rule

Always validate arrays with dive


Emails []string `validate:"required,dive,email"`

Use cross-field validation for related fields


StartDate time.Time `validate:"required"`
EndDate   time.Time `validate:"required,gtefield=StartDate"`

Quick Reference Card

Most Used Validation Tags


// Required field
Field string `validate:"required"`
 
// Optional (validate only if present)
Field string `validate:"omitempty,email"`
 
// String constraints
Field string `validate:"min=5,max=20"`
Field string `validate:"email"`
Field string `validate:"url"`
Field string `validate:"alpha"`
Field string `validate:"alphanum"`
 
// Number constraints
Field int `validate:"gte=18,lte=120"`
Field int `validate:"gt=0"`
Field int `validate:"oneof=1 2 3 4 5"`
 
// Arrays
Field []string `validate:"required,min=1,max=5"`
Field []string `validate:"dive,email"` // Each element must be email
 
// Cross-field validation
Password        string `validate:"required"`
ConfirmPassword string `validate:"eqfield=Password"`
 
// Conditional validation
ShipDifferent bool   `validate:"boolean"`
ShipAddress   string `validate:"required_if=ShipDifferent true"`
 
// Enum validation
Role string `validate:"oneof=admin user guest"`