@assert

The @assert attribute in BAML is used for strict validations. If a type fails an @assert validation, it will not be returned in the response, and an exception will be raised if it’s part of the top-level type.

Usage

Asserts can be named or unnamed.

Field Assertion

BAML

1 class Foo {
2   // @assert will be applied to the field with the name "bar"
3   bar int @assert(between_0_and_10, {{ this > 0 and this < 10 }})
4 }

BAML

1 class Foo {
2   // @assert will be applied to the field with no name
3   bar int @assert({{ this > 0 and this < 10 }})
4 }

BAML

1 class MyClass {
2   // @assert will be applied to each element in the array
3   my_field (string @assert(is_valid_email, {{ this|regex_match("@") }}))[]
4 }

Parameter Assertion

Asserts can also be applied to parameters.

BAML

1 function MyFunction(x: int @assert(between_0_and_10, {{ this > 0 and this < 10 }})) {
2   client "openai/gpt-4o"
3   prompt #"Hello, world!"#
4 }

Block Assertion

Asserts can be used in a block definition, referencing fields within the block.

BAML

1 class Foo {
2   bar int
3   baz string
4   @@assert(baz_length_limit, {{ this.baz|length < this.bar }})
5 }

See Jinja in Attributes for a longer description of the Jinja syntax available in asserts.

1	class Foo {
2	// @assert will be applied to the field with the name "bar"
3	bar int @assert(between_0_and_10, {{ this > 0 and this < 10 }})
4	}

1	class Foo {
2	// @assert will be applied to the field with no name
3	bar int @assert({{ this > 0 and this < 10 }})
4	}

1	class MyClass {
2	// @assert will be applied to each element in the array
3	my_field (string @assert(is_valid_email, {{ this\|regex_match("@") }}))[]
4	}

1	function MyFunction(x: int @assert(between_0_and_10, {{ this > 0 and this < 10 }})) {
2	client "openai/gpt-4o"
3	prompt #"Hello, world!"#
4	}

1	class Foo {
2	bar int
3	baz string
4	@@assert(baz_length_limit, {{ this.baz\|length < this.bar }})
5	}