Built-in Processors

A reference for all built-in value processors available via $keyword syntax.

Processor	Description
$abs	Returns the absolute value of a number.
$all	A constraint that checks whether all the provided processors return a defined value.
$alpha	Validates that a string contains only alphabetic characters (a-z, A-Z). No spaces, numbers, punctuation, or special char
$alphanum	Validates that a string contains only alphanumeric characters (A-Z, a-z, 0-9). No spaces, punctuation, or special charac
$and	A constraint that checks whether all the provided processors return a truthy value.
$any	A constraint that checks whether any of the provided processors return a defined value. (Not to be confused with the unr
$array	Attempt to normalize the input value as an array.
$assert	Require that the provided processor returns a truthy value; return original input. Throws a constraint exception if not
$base64	Validates that a string is properly formatted Base64 encoded data. Checks for valid Base64 character set (A-Z, a-z, 0-9,
$base64-decode	Decodes a Base64-encoded string to a Buffer. Throws if the input is not a string.
$base64-encode	Encodes a Buffer to a Base64 string. Throws if the input is not a Buffer.
$buffer	Converts a value to a Node.js Buffer. Accepts: - Buffer — passed through unchanged - string — decoded from Base64 via B
$camel-case	Converts a string value to camelCase format. Words are identified by spaces, hyphens, underscores, or case changes. The
$capitalize	Capitalizes the first letter of each word, separated by spaces. Words are split on non-alphanumeric boundaries (spaces,
$cardnum	Validates a payment card number (PAN) using the Luhn algorithm and normalizes its formatting based on the detected card
$ceil	Rounds a numeric value up to the nearest integer or specified decimal precision. Non-numeric values are passed through u
$check	This is a conditional operator that evaluates a predicate for truthiness.
$clamp	Constrains a number to a [min, max] range by returning the nearest boundary when the value falls outside. Unlike $range
$collapse	Collapses runs of whitespace within a string to a single space, and trims leading and trailing whitespace. Useful for no
$compact	Strips common formatting characters from a string: whitespace, hyphens, dots, parentheses, and forward slashes. Useful f
$compile	Compiles a Schema (or CompiledSchema) into a CompiledSchema ready for use in value processing. If a schema argument is p
$concat	Returns a new array with the specified values appended to the input array. Throws SchemaError at compile time if no argu
$constant-case	Converts a string to CONSTANT_CASE format (uppercase letters with underscores). Safe to use in normalize phase (non-thro
$date	Normalize the input value as a Date. Accepts strings, numbers, Date instances, and date-field objects produced by $date
$date-object	Expands a Date into a plain object with named calendar fields.
$date-range	Validates that a date value falls within the specified range (inclusive). Can specify minimum, maximum, or both bounds.
$defined	Allow any value, as long as it's defined.
$directory	Validates that a path exists on the filesystem and is a directory (not a file). This is an async processor that performs
$each	Applies a processor to each element of an array. The processor can be any valid processor specification (RegExp, functio
$email	Validates that a string matches a practical email address format (local-part@domain.tld).
$entries	Returns the enumerable own properties of an object as an array of [key, value] pairs, matching the output of Object.entr
$eq	Do a deep equality check between the value and the provided constraint value.
$exclusive	A constraint that checks whether exactly one of the provided processors returns a truthy value.
$executable	Validates that a file path points to an executable file by checking execute permissions. This is an asynchronous process
$file	Validates that a path exists in the filesystem and is a file (not a directory or other type). Performs an asynchronous f
$file-size	Validates that a file's size falls within the specified range. Accepts size constraints in bytes and checks the file's m
$filter	Runs a processor on each element of the input array, keeping elements for which the processor succeeds and returning the
$find-schema	Find a schema in the schema hierarchy based on a dotted path. Returns the current schema by default. The provided path
$first	An operator that returns the first defined value successfully returned from a sequence of processors.
$flatten	Returns a new array with sub-array elements flattened to the specified depth. Throws if the input is not an array.
$floor	Rounds a numeric value down to the specified number of decimal places. Non-numeric values are passed through unchanged.
$gate	This is a conditional operator that evaluates a predicate for whether it returns a defined value.
$get	Extracts a value from the input using a dot-separated path (for objects) or a numeric index (for arrays). Does not requi
$group-by	Groups an array of objects by a key, returning an object whose values are arrays of elements that share that key value.
$has-prefix	Check that the provided string value starts with the prefix value
$has-suffix	Check that the provided string value ends with the suffix value
$hex	Validates that a string contains only valid hexadecimal characters (0-9, a-f, A-F). Does not require or validate a "0x"
$hostname	Validates that a string matches valid hostname format according to RFC 1123. Hostnames must start and end with alphanume
$http-url	Validates that a string is a valid HTTP or HTTPS URL. Uses the URL Web API for validation and specifically requires the
$if	This is a conditional operator that evaluates a predicate for truthiness.
$in	Validates that a value is included in an allowed list of values. Uses strict equality (===) for comparison.
$index-by	Groups an array of objects by a unique key, returning an object whose value is the single array element value that has t
$input	Returns the input value passed to the processor. Acts as a declarative "pass-through". Useful for passing the input to
$instanceof	Validates that the input is an instance of the specified constructor.
$integer	Validates that a numeric value is an integer (no fractional part). Input must already be a number; use $number in a prio
$invoke	Calls a provided processor and passes it arguments (if any).
$ipv4	Validates that a string is a valid IPv4 address in dotted-decimal notation.
$ipv6	Validates that a string is a properly formatted IPv6 address. Supports all standard notation formats including full, com
$is-array	Validates that the input is a valid array.
$is-buffer	Validates that the input is a Node.js Buffer.
$is-date	Validates that the input is a valid date.
$is-number	Validates that the input is a valid number.
$is-object	Validates that the input is a valid object (and not null!)
$is-string	Validates that the input is a valid string.
$join	Join the input array elements into a string using the provided separator.
$json	Validates that a string contains valid JSON that can be parsed by JSON.parse(). The processor does not modify the input
$json-decode	Parses a JSON string into a value. Throws if the input is not a string or is not valid JSON.
$json-encode	Serializes any value to a JSON string.
$kebab-case	Converts a string to kebab-case format (lowercase words separated by hyphens). Safe to use in normalize phase (non-throw
$keys	Returns the enumerable own property keys of an object as an array of strings. Throws if the input is not a plain object.
$length	Validates that the length of a string or array falls within specified bounds (inclusive). Can specify minimum, maximum,
$lookup	Uses the pipeline value as a key to look up a corresponding value from the argument collection. This is the inverse of $
$lowercase	Converts a string value to lowercase. Safe to use in normalize phase (non-throwing).
$map	Polymorphic map operator. Applies a processor to each element of an array, or to each value of a plain object. Returns a
$match	Operator that executes a RegExp match against a string input and returns the extracted result. Non-string values are pas
$matches	Constraint that tests the string representation of the input against a RegExp. Throws a ConstraintError if the input doe
$max	Returns the maximum value from an array of numbers. Returns undefined for an empty array.
$merge	Merges the argument object into the input object (shallow). The argument fields take precedence over same-named fields i
$merge-deep	Recursively deep-merges the argument object into the input object, returning a new object. Nested plain objects are merg
$metadata	Extracts named metadata from a schema, either from the current schema or a parameter.
$min	Returns the minimum value from an array of numbers. Returns undefined for an empty array.
$negative	Validates that a numeric value is negative (less than 0). Input must already be a number; use $number in a prior normali
$never	Inverts a processor - Returns the input if the wrapped processor throws or returns an undefined value. Throw a constrain
$non-empty	Validates that a string, array, or object is not empty. For strings, the value must contain at least one non-whitespace
$normalize	Normalize the incoming value according using the provided schema
$not	Inverts a processor result - returns true if the wrapped processor throws or returns a falsey value. Throw a constraint
$number	Validates and coerces values to numbers. Accepts numeric strings, integers, and floats. Rejects NaN, Infinity, and non-n
$numeric	Validates that a string contains only numeric digits (0-9). The value is coerced to a string before validation, so numbe
$object	Attempts to normalize the input value as an object.
$omit	Returns a new object or dense array with the specified keys/indices removed. Keys not present in the input are silently
$one	A constraint that checks whether exactly one of the provided processors returns a defined value.
$or	A constraint that checks whether any of the provided processors return a truthy value.
$pad	Pads a string to a minimum width.
$parallel	Applies an array of processors concurrently to the same input value, returning an array of all results in the same order
$pascal-case	Converts a string value to PascalCase format (first letter of each word capitalized, no separators). Safe to use in norm
$phone	Validates and normalizes a phone number string.
$pick	Returns a new object or dense array containing only the specified keys/indices from the input. Keys not present in the i
$pipeline	Executes a sequence of processors in order, passing the output of each processor as input to the next. The final process
$port	Validates that a value is a valid TCP/UDP port number (1-65535). Accepts numeric values or strings that can be converted
$positive	Validates that a numeric value is positive (greater than 0). Input must already be a number; use $number in a prior norm
$pow	Raises a number to a power.
$process	Process the incoming value according to the provided schema
$property	Extracts a named property value from an object. This operator is useful for accessing nested properties or extracting sp
$range	Validates that a numeric value falls within the specified range (inclusive). Can specify minimum, maximum, or both bound
$reachable	Validates that a hostname is reachable by performing a DNS lookup. This is an asynchronous processor that checks if the
$readable	Validates that a file or directory path exists and has read permissions for the current process. Performs an asynchronou
$reference	Returns the value at the referenced path (relative to the current schema) in the target data, or undefined if not set.
$replace	Replaces occurrences of a pattern in a string.
$require	Require that the provided processor returns a defined value; return the original input if so. Throws a constraint error
$reverse	Returns a new array with elements in reverse order. Non-mutating. Throws if the input is not an array.
$round	Rounds a numeric value to the nearest integer or to a specified number of decimal places. Safe to use in normalize phase
$semver	Validates that a string is a valid semantic version per the semver 2.0.0 spec.
$sort	Returns a new sorted array. Non-mutating. Numbers are compared numerically; all other values are compared lexicographica
$split	Stringify the input and split on the provided separator, returning an array.
$sqrt	Returns the square root of a number.
$string	Ensures value is a string, stringifying as necessary. Everything other than null and undefined can be converted.
$substring	Extracts a portion of a string by start index and optional length.
$sum	Returns the sum of an array of numbers. Returns 0 for an empty array.
$target	Returns the target value passed to the processor (value being built relative to the root). (Note: may return undefined o
$template	Operator that interpolates a template string using properties from the input object. Placeholders use {key} syntax; do
$title-case	Converts a string to title case, capitalizing the first letter of each significant word and leaving articles, coordinati
$trim	Removes leading and trailing whitespace from a string value. Safe to use in normalize phase (non-throwing operator).
$truthy	Validates that the value is "truthy". Note that the definition of what values are "truthy" mirrors the boolean schema n
$try	This is a conditional operator that evaluates a predicate for whether it throws/rejects.
$type	Returns the type name of the input value as a string. Unlike the $is-* constraint family, this operator produces the typ
$unique	Returns a new array with duplicate values removed, preserving insertion order of first occurrences. Uses identity-based
$uppercase	Converts a string value to uppercase. Safe to use in normalize phase (non-throwing). Non-string values are coerced to st
$url	Validates that a string is a valid URL and normalizes it to canonical form. Uses the WHATWG URL Standard for validation
$url-decode	Decodes a percent-encoded URL string.
$url-encode	Percent-encodes a string for safe use as a URL component (query param value, path segment, etc.). Encodes all characters
$uuid	Validates that a string matches valid UUID format (versions 1-5). UUIDs must follow RFC 4122 format: 8-4-4-4-12 hexadeci
$values	Returns the enumerable own property values of an object as an array. Throws if the input is not a plain object.
$when	This is a conditional operator that evaluates a predicate for whether it returns a defined value.
$writable	Validates that a file system path is writable by checking write permissions. If the path does not exist, validates that