Built-in Rules Reference

Here is a complete list of all types and validators available out of the box.

Built-in Types (Casting Rules)

A field's type defines how the input value will be converted before any other validation rules are run.

Type Name	Description
string	Converts the input to a string. By default, it trims whitespace. Fails if the input is an object or array.
number	Converts the input to a finite number. Empty strings, whitespace-only strings, and non-finite values fail validation.
integer	Converts the input to a finite integer. Non-integer numeric values fail validation.
boolean	Converts the input to a boolean using explicit true/false tokens such as true, false, 1, 0, yes, no, on, and off. Unknown values fail validation.
array	Ensures the value is an array. If the input is not already an array, it will be wrapped in one (e.g., 'tag1' becomes ['tag1']). If items is present, every item is validated recursively.
id	Parses the value into a positive safe integer identifier. It rejects non-canonical forms such as leading zeroes or strings with junk suffixes.
date	Converts a valid date string or timestamp into a Date object normalized to midnight UTC for that calendar day.
dateTime	Converts a valid date string or timestamp into a Date object. MySQL-style YYYY-MM-DD HH:MM:SS strings are interpreted as UTC.
timestamp	Converts the input to a number, suitable for storing Unix timestamps.
time	Converts the input to a normalized HH:MM:SS string.
serialize	Converts any JavaScript value (including objects with circular references) into a single JSON-like string using flatted.
object	Requires a plain object value. With schema, it becomes a nested object contract. With values, it becomes a typed object map. With additionalProperties: true, it becomes either an opaque pass-through object bag or a passthrough nested object when combined with schema. Without any of those options, it is simply a validated plain object value with no child-field rules.
blob	Passes the value through unchanged. Intended for binary data like files that don't need casting.
file	Converts primitive file-handle-like values to strings and rejects objects or arrays.
none	The "identity" type. Passes the value through completely unchanged without any casting.

Built-in Validators (Validation Parameters)

Validators are rules that run after a value has been cast to its proper type.

Parameter	Description
required: true	The field must be present in the input object. Fails if the key is undefined.
minLength: <number>	For string types, validates the minimum character length.
maxLength: <number>	For string types, validates the maximum character length.
min: <number>	For number types, validates the minimum value.
max: <number>	For number types, validates the maximum value.
enum: <array>	Restricts the field to one of the declared values. Exported as a standard JSON Schema enum.
notEmpty: true	The field cannot be an empty string (''). This is different from required, as an empty string is still a defined value.
length: <number>	For string types, it truncates the string to the specified length. For number types, it throws an error if the number of digits in the original input exceeds the specified length.
nullable: true	Allows the value for this field to be null. By default, null is not allowed.
nullOnEmpty: true	If the input value is an empty string (''), it will be cast to null before other validators run.
lowercase: true	Transforms the string to all lowercase.
uppercase: true	Transforms the string to all uppercase.
strictBoolean: true	Restricts a boolean field so the original input must already be a real boolean.
validator: <function>	Allows you to provide your own synchronous custom validation function for complex, one-off logic.
defaultTo: <value>	If the field is not present in the input object, this value will be used in validation modes that apply defaults. Can be a value or a function that returns a value.
unsigned: true	Passive schema metadata indicating non-negative numeric storage intent. Preserved in transport export metadata.
precision: <number>	Passive schema metadata for decimal total digits. Preserved in transport export metadata.
scale: <number>	Passive schema metadata for decimal fractional digits. Preserved in transport export metadata.
temporalPrecision: <number>	Passive schema metadata for time or datetime fractional-second precision. Preserved in transport export metadata.

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