Implementation:Guardrails ai Guardrails RailTypes

Knowledge Sources	Guardrails
Domains	Types, RAIL
Last Updated	2026-02-14 00:00 GMT

Overview

Defines the RailTypes enumeration representing all built-in data types supported by the RAIL XML specification.

Description

The RailTypes class is a string enumeration (str, Enum) that maps human-readable type names to their RAIL XML tag values. It supports thirteen data types that cover primitive values (strings, integers, floats, booleans), temporal values (dates, times, datetimes), structural values (lists, objects), and special types (percentages, enums, discriminated unions via choice/case).

Because RailTypes inherits from both str and Enum, each member can be used directly as a string wherever a RAIL type name is expected. The class also provides a get classmethod for safe lookup that returns None instead of raising an exception when a key is not found.

Usage

Use RailTypes when parsing or constructing RAIL XML documents to validate that a given type string corresponds to a recognized built-in type. The get classmethod is particularly useful for safely checking if a tag name is a known RAIL type without exception handling.

Code Reference

Source Location

• Repository: Guardrails
• File: guardrails/types/rail.py

Signature

class RailTypes(str, Enum):
    STRING = "string"
    INTEGER = "integer"
    FLOAT = "float"
    BOOL = "bool"
    DATE = "date"
    TIME = "time"
    DATETIME = "date-time"
    PERCENTAGE = "percentage"
    ENUM = "enum"
    LIST = "list"
    OBJECT = "object"
    CHOICE = "choice"
    CASE = "case"

    @classmethod
    def get(cls, key: str) -> Optional["RailTypes"]: ...

Import

from guardrails.types.rail import RailTypes

I/O Contract

Enum Members

Member	Value	Description
STRING	"string"	A string value
INTEGER	"integer"	An integer value
FLOAT	"float"	A float value
BOOL	"bool"	A boolean value
DATE	"date"	A date value
TIME	"time"	A time value
DATETIME	"date-time"	A datetime value
PERCENTAGE	"percentage"	A percentage value represented as a string (e.g. "20.5%")
ENUM	"enum"	An enum value
LIST	"list"	A list/array value
OBJECT	"object"	An object/dictionary value
CHOICE	"choice"	The options for a discriminated union
CASE	"case"	A dictionary that contains a discriminated union

get Classmethod

Parameter	Type	Description
key	str	The RAIL type string to look up

Returns: Optional[RailTypes] -- The matching enum member, or None if no match is found.

Usage Examples

from guardrails.types.rail import RailTypes

# Direct access
rail_type = RailTypes.STRING
print(rail_type)         # "string"
print(rail_type.value)   # "string"

# Safe lookup
result = RailTypes.get("integer")
print(result)  # RailTypes.INTEGER

# Safe lookup with unknown type
result = RailTypes.get("unknown_type")
print(result)  # None

# Use as string
if RailTypes.get("date-time") is not None:
    print("date-time is a valid RAIL type")

Related Pages

• Guardrails_ai_Guardrails_RAIL_Schema -- Uses RailTypes for parsing RAIL XML documents
• Guardrails_ai_Guardrails_Types -- Parent types module