Implementation:Guardrails ai Guardrails OutputTypes

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

Overview

The OutputTypes enumeration defines the three possible output types for Guard validation results: STRING, LIST, and DICT.

Description

This module provides the OutputTypes enum which extends both str and Enum. It is used throughout the Guardrails framework to classify the expected shape of validated LLM output. The enum provides:

• Three members: STRING ("str"), LIST ("list"), and DICT ("dict").
• get static method: A safe accessor that returns the matching OutputTypes member or a default value, handling None and invalid keys gracefully.
• __from_json_schema__ class method: Derives the output type from a JSON Schema definition by inspecting the type, allOf, oneOf, and anyOf fields. Defaults to STRING as a fallback.

The module also defines the OT TypeVar (TypeVar("OT", str, List, Dict)) for generic typing of output values.

Usage

Use OutputTypes whenever you need to determine or specify the expected output format for a Guard. It is used by action handlers (like apply_refrain) to produce correctly typed empty values, and by the core validation pipeline to route output processing.

Code Reference

Source Location

• Repository: Guardrails
• File: guardrails/classes/output_type.py
• Lines: 1-63

Signature

OT = TypeVar("OT", str, List, Dict)

class OutputTypes(str, Enum):
    STRING = "str"
    LIST = "list"
    DICT = "dict"

    @staticmethod
    def get(key: Optional[Union[str, "OutputTypes"]], default=None):

    @classmethod
    def __from_json_schema__(cls, json_schema: Dict[str, Any]) -> "OutputTypes":

Import

from guardrails.classes.output_type import OutputTypes, OT

I/O Contract

Enum Members

Member	Value	Description
STRING	"str"	Output is a plain string.
LIST	"list"	Output is a list.
DICT	"dict"	Output is a dictionary.

get

Parameter	Type	Description
key	Optional[Union[str, OutputTypes]]	The key to look up. Can be a string name, an OutputTypes member, or None.
default	Any	Value to return if the key does not match any member. Defaults to None.

Return Type	Description
Optional[OutputTypes]	The matching OutputTypes member, or the default value.

__from_json_schema__

Parameter	Type	Description
json_schema	Dict[str, Any]	A JSON Schema dictionary to derive the output type from.

Return Type	Description
OutputTypes	The inferred output type based on the schema's type, allOf, oneOf, or anyOf fields. Falls back to STRING.

JSON Schema Mapping

JSON Schema Type	OutputTypes Result
string	STRING
object	DICT
array	LIST
Has allOf	DICT
Has oneOf	Recursively resolves first sub-schema
Has anyOf	Recursively resolves first sub-schema
(fallback)	STRING

Usage Examples

from guardrails.classes.output_type import OutputTypes

# Direct member access
output_type = OutputTypes.DICT
print(output_type.value)  # "dict"

# Safe lookup with get
output_type = OutputTypes.get("STRING")
# output_type: OutputTypes.STRING

output_type = OutputTypes.get(None, default=OutputTypes.STRING)
# output_type: OutputTypes.STRING

# Derive from JSON Schema
schema = {"type": "object", "properties": {"name": {"type": "string"}}}
output_type = OutputTypes.__from_json_schema__(schema)
# output_type: OutputTypes.DICT

# Array schema
schema = {"type": "array", "items": {"type": "string"}}
output_type = OutputTypes.__from_json_schema__(schema)
# output_type: OutputTypes.LIST

Related Pages

• Guardrails_ai_Guardrails_Refrain_Action - Uses OutputTypes to determine the empty replacement value when refraining
• Guardrails_ai_Guardrails_Filter_Action - Uses output type context during filter processing