Validation tags

EchoNext uses go-playground/validator rules in the validate struct tag.

type CreatePost struct {
    Title  string   `json:"title" validate:"required,min=3,max=200"`
    Email  string   `json:"email" validate:"required,email"`
    Status string   `json:"status" validate:"oneof=draft published"`
    Tags   []string `json:"tags" validate:"max=5,dive,min=2,max=20"`
}

Frequently used rules include required, omitempty, min, max, len, email, url, uuid, oneof, and dive for collection elements.

Validation checks syntax and local invariants. Authorization, database uniqueness, ownership, and cross-record business rules still belong in application logic.