Built-in rules

Every built-in rule, by category. Params go next to rule in a field's rules, and every rule also takes a message. A rule with params per kind lists them by kind. The validation rules guide explains how they run.

Length

Rule	Label	Kinds	Params	Description
length	Exact length	string, array	value: integer, at least 0
minLength	Minimum length	string, array	value: integer, at least 0
maxLength	Maximum length	string, array	value: integer, at least 0
notLength	Not this length	string, array	value: integer, at least 0

Text

Rule	Label	Kinds	Params	Description
graphemes	Exact characters	string	value: integer, at least 0	Counts characters as people see them, so an emoji is one.
minGraphemes	Minimum characters	string	value: integer, at least 0	Counts characters as people see them, so an emoji is one.
maxGraphemes	Maximum characters	string	value: integer, at least 0	Counts characters as people see them, so an emoji is one.
notGraphemes	Not this many characters	string	value: integer, at least 0	Counts characters as people see them, so an emoji is one.
words	Exact words	string	locale?: string; value: integer, at least 0
minWords	Minimum words	string	locale?: string; value: integer, at least 0
maxWords	Maximum words	string	locale?: string; value: integer, at least 0
notWords	Not this many words	string	locale?: string; value: integer, at least 0
bytes	Exact bytes	string	value: integer, at least 0	Counts UTF-8 bytes, e.g. to fit a database column.
minBytes	Minimum bytes	string	value: integer, at least 0	Counts UTF-8 bytes, e.g. to fit a database column.
maxBytes	Maximum bytes	string	value: integer, at least 0	Counts UTF-8 bytes, e.g. to fit a database column.
notBytes	Not this many bytes	string	value: integer, at least 0	Counts UTF-8 bytes, e.g. to fit a database column.

Content

Rule	Label	Kinds	Params	Description
regex	Matches pattern	string	pattern: string; flags?: string	A JavaScript regular expression, without the slashes.
startsWith	Starts with	string	value: string
endsWith	Ends with	string	value: string
includes	Contains	string, array	string: value: string array: value: string | number | boolean
excludes	Does not contain	string, array	string: value: string array: value: string | number | boolean

Format

Rule	Label	Kinds	Params	Description
email	Email	string
rfcEmail	Email (RFC 5322)	string
url	URL	string
domain	Domain	string
slug	Slug	string
uuid	UUID	string
ulid	ULID	string
cuid2	CUID2	string
nanoid	Nano ID	string
ip	IP address	string
ipv4	IPv4 address	string
ipv6	IPv6 address	string
mac	MAC address	string
mac48	MAC-48 address	string
mac64	MAC-64 address	string
hexColor	Hex colour	string
hexadecimal	Hexadecimal	string
octal	Octal	string
decimal	Decimal number	string
digits	Digits only	string
base64	Base64	string
bic	BIC (SWIFT code)	string
creditCard	Credit card number	string
imei	IMEI	string
isbn	ISBN	string
isrc	ISRC	string
emoji	Emoji	string
hash	Hash	string	types: ("md4" | "md5" | "sha1" | "sha256" | "sha384" | "sha512" | "ripemd128" | "ripemd160" | "tiger128" | "tiger160" | "tiger192" | "crc32" | "crc32b" | "adler32")[], at least 1

Date

Rule	Label	Kinds	Params	Description
isoDate	ISO date	string, date		Like 2026-10-28
isoDateTime	ISO date and time	string, date		Like 2026-10-28T14:30
isoTime	ISO time	string, date		Like 14:30
isoTimeSecond	ISO time with seconds	string, date		Like 14:30:15
isoTimestamp	ISO timestamp	string, date		Like 2026-10-28T14:30:15.000Z
isoWeek	ISO week	string, date		Like 2026-W44

Comparison

Rule	Label	Kinds	Params	Description
minValue	Minimum	number, date	number: value: number date: value: string
maxValue	Maximum	number, date	number: value: number date: value: string
gtValue	Greater than	number, date	number: value: number date: value: string
ltValue	Less than	number, date	number: value: number date: value: string
value	Equals	number, date, string, boolean	number: value: number date: value: string string: value: string boolean: value: boolean
notValue	Does not equal	number, date, string, boolean	number: value: number date: value: string string: value: string boolean: value: boolean
values	One of	number, date	number: values: number[], at least 1 date: values: string[], at least 1
notValues	None of	number, date	number: values: number[], at least 1 date: values: string[], at least 1

Number

Rule	Label	Kinds	Params	Description
integer	Whole number	number
safeInteger	Safe whole number	number
finite	Finite number	number
multipleOf	Multiple of	number	value: number

File

Rule	Label	Kinds	Params	Description
minSize	Minimum size	file	value: integer, at least 0	In bytes, e.g. 1048576 for 1 MiB.
maxSize	Maximum size	file	value: integer, at least 0	In bytes, e.g. 1048576 for 1 MiB.
size	Exact size	file	value: integer, at least 0	In bytes, e.g. 1048576 for 1 MiB.
notSize	Not this size	file	value: integer, at least 0	In bytes, e.g. 1048576 for 1 MiB.
mimeType	File type	file	types: string[], at least 1

Normalize

Rule	Label	Kinds	Params	Description
trim	Trim	string
trimStart	Trim start	string
trimEnd	Trim end	string
toLowerCase	Lowercase	string
toUpperCase	Uppercase	string
normalize	Unicode normalize	string	form?: "NFC" | "NFD" | "NFKC" | "NFKD"	Defaults to NFC.
toMinValue	Raise to minimum	number	value: number	Replaces a smaller number with the minimum.
toMaxValue	Lower to maximum	number	value: number	Replaces a larger number with the maximum.

Form rules

These go in formRules, next to fields. Each one also takes field, the path its error shows on, and message. See the form rules guide.

Rule	Label	Kinds	Params	Description
sameAs	Same as	string, number, boolean, date	other: string	Equals another field, e.g. to confirm a password
differentFrom	Different from	string, number, boolean, date	other: string	Differs from another field, e.g. a new password
compare	Compare	number, date	op: "lt" | "lte" | "gt" | "gte"; other: string	Less or greater than another field, e.g. an end date after the start