BAML Error Types

BAML provides error classes for handling different error scenarios when working with LLMs.

Error Class Hierarchy

All BAML errors extend the base Error class and include a literal type field.

// BAML-specific error classes
class BamlValidationError extends Error {
  type: 'BamlValidationError'
  message: string
  prompt: string
  raw_output: string
  detailed_message: string
}

class BamlClientFinishReasonError extends Error {
  type: 'BamlClientFinishReasonError'
  message: string
  prompt: string
  raw_output: string
  detailed_message: string
}

class BamlAbortError extends Error {
  type: 'BamlAbortError'
  message: string
  reason?: any
  detailed_message: string
}

Error Types

Error	Description
BamlValidationError	Failed to parse or validate LLM output
BamlClientFinishReasonError	LLM terminated with disallowed finish reason
BamlAbortError	Operation cancelled via abort controller

Fallback Error Aggregation

When using fallback clients or clients with retry policies, BAML attempts multiple client calls before failing:

• The error type corresponds to the final (last) failed attempt
• The message field contains the error message from the final attempt
• The detailed_message field contains the complete history of all failed attempts

Type Guards

TypeScript

import { BamlAbortError, BamlValidationError, BamlClientFinishReasonError } from '@boundaryml/baml'

try {
  const result = await b.MyFunction(input)
} catch (error) {
  if (error instanceof BamlAbortError) {
    // Handle cancellation
  } else if (error instanceof BamlValidationError) {
    // Handle validation error
  } else if (error instanceof BamlClientFinishReasonError) {
    // Handle finish reason error
  }
}

Python

from baml_py import BamlAbortError, BamlValidationError, BamlClientFinishReasonError

try:
    result = await b.MyFunction(input)
except BamlAbortError as e:
    # Handle cancellation
except BamlValidationError as e:
    # Handle validation error
except BamlClientFinishReasonError as e:
    # Handle finish reason error

Common Properties

Property	Type	Description
type	string	Literal type identifier for each error class
message	string	Human-readable error message
detailed_message	string	Complete history of all failed attempts when using fallback/retry