Built-in rules

Every rule of the LIVR specification is built in. This page is a short list with the TypeScript type of every rule. The full reference, with the arguments, error codes and examples of every rule, is on the specification site:

All validation rules ↗︎ Every rule with its arguments, error codes and examples. Opens livr-spec.org, the site of the LIVR specification.

Rule names below link to their pages in the specification. The last column shows the TypeScript type that InferFromSchema gives a field with this rule.

Rule names work in snake_case and in camelCase: min_length and minLength are the same rule.

Common rules

Rule	Checks	Type
required	The value is present: not missing, not null and not an empty string. 0 and false are valid	makes the field required
not_empty	The value is not an empty string, if the field is passed at all	string
not_empty_list	The value is a list with at least one element	unknown[]
any_object	The value is a plain object, its content is not validated	Record<string, unknown>

String rules

Rule	Checks	Type
string	The value is a primitive, returned as a string	string
eq	The value equals the given one	the literal
one_of	The value is one of the allowed values	a union of the literals
max_length	The string is not longer than the given length	string
min_length	The string is at least the given length	string
length_between	The length is between two values, inclusive	string
length_equal	The string has exactly the given length	string
like	The value matches a regular expression	string

Numeric rules

Numeric rules accept strings that look like numbers, such as '42' from a form, and return numbers.

Rule	Checks	Type
integer	The value is an integer	number
positive_integer	The value is an integer greater than zero	number
decimal	The value is a number, an integer or a decimal	number
positive_decimal	The value is a number greater than zero	number
max_number	The number is not greater than the given value	number
min_number	The number is not less than the given value	number
number_between	The number is between two values, inclusive	number

Special rules

Rule	Checks	Type
email	The value is an email address	string
url	The value is an http or https URL	string
iso_date	The value is an ISO 8601 date without time, like 2014-08-14	string
equal_to_field	The value equals another field, like a password confirmation	string

Metarules

Metarules describe nested data with other rules.

Rule	Describes	Type
nested_object	A nested object	the object type
variable_object	An object whose rules depend on a selector field	a union of the object types
list_of	A list, the rules apply to every element	an array
list_of_objects	A list of objects	an array of the object type
list_of_different_objects	A list of objects whose rules depend on a selector field	an array of the union
or	Alternatives: the first set of rules that succeeds wins	a union

Modifiers

Modifiers change the output and never return errors.

Rule	Does	Type
trim	Removes leading and trailing whitespace	string
to_lc	Converts to lower case	string
to_uc	Converts to upper case	string
remove	Removes the given characters	string
leave_only	Removes all characters except the given ones	string
default	Sets a value when the value is empty	the type of the default, field becomes required

More rules

livr-extra-rules adds boolean, ipv4, uuid, credit_card, iso_date with ranges, required_if, list_length and more. You can also write your own.