ctx.output_format

The prefix instruction to use before printing out the schema.

Answer in this schema correctly I'll tip $400:
{
  ...
}

BAML’s default prefix varies based on the function’s return type.

Whether to inline the enum definitions in the schema, or print them above. Default: false

Note that setting this to false means BAML will use heuristics internally to determine whether or not to hoist. false does not mean “never hoist”.

Inlined

Answer in this json schema:
{
  categories: "ONE" | "TWO" | "THREE"
}

hoisted

MyCategory
---
ONE
TWO
THREE
Answer in this json schema:
{
  categories: MyCategory
}

Default: or

If a type is a union like string | int or an optional like string?, this indicates how it’s rendered.

BAML renders it as property: string or null as we have observed some LLMs have trouble identifying what property: string | null means (and are better with plain english).

You can always set it to | or something else for a specific model you use.

Default: "auto"

Controls which classes are hoisted in the prompt. Recursive classes are always hoisted because they need to be referenced by name.

Let’s use this as an example to visualize the different options:

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class Example {
2
  a string
3
  b string
4
  c NestedClass
5
  d Node
6
}
7
8
class NestedClass {
9
  m int
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  n int
11
}
12
13
class Node {
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  data int
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  next Node?
16
}
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18
function UseExample() -> Example {
19
  client GPT4
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  prompt #"{{ctx.output_format}}"#
21
}

“auto”

Only recursive classes are hoisted:

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Node {
2
  data: int,
3
  next: Node or null
4
}
5
6
Answer in JSON using this schema:
7
{
8
  a: string,
9
  b: string,
10
  c: {
11
    m: int,
12
    n: int,
13
  },
14
  d: Node,
15
}

false

Same as "auto".

true

Hoist all classes.

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Node {
2
  data: int,
3
  next: Node or null
4
}
5
6
Example {
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  a: string,
8
  b: string,
9
  c: NestedClass,
10
  d: Node,
11
}
12
13
NestedClass {
14
  m: int,
15
  n: int,
16
}
17
18
Answer in JSON using this schema: Example

list[string]

Hoist only recursive classes and the classes specified in the list. For example ctx.output_format(hoist_classes=["NestedClass"]) will hoist NestedClass.

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Node {
2
  data: int,
3
  next: Node or null
4
}
5
6
NestedClass {
7
  m: int,
8
  n: int,
9
}
10
11
Answer in JSON using this schema:
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{
13
  a: string,
14
  b: string,
15
  c: NestedClass,
16
  d: Node,
17
}

Prefix of hoisted classes in the prompt. Default: <none>

This parameter controls the prefix used for hoisted classes as well as the word used in the render message to refer to the output type, which defaults to "schema":

Answer in JSON using this schema:

See examples below.

Recursive BAML Prompt Example

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class Node {
2
  data int
3
  next Node?
4
}
5
6
class LinkedList {
7
  head Node?
8
  len int
9
}
10
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function BuildLinkedList(input: int[]) -> LinkedList {
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  prompt #"
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    Build a linked list from the input array of integers.
14
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    INPUT: {{ input }}
16
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    {{ ctx.output_format }}    
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  "#
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}

Default hoisted_class_prefix (none)

Node {
  data: int,
  next: Node or null
}
Answer in JSON using this schema:
{
  head: Node or null,
  len: int
}

Custom Prefix: hoisted_class_prefix="interface"

interface Node {
  data: int,
  next: Node or null
}
Answer in JSON using this interface:
{
  head: Node or null,
  len: int
}