Provider Comparison

Every structured output provider supports a different subset of JSON Schema. This page shows where they diverge so you can pick the right one for your schema. The table only includes features where at least one provider differs. Basic types, items, and $defs / $ref are supported by all four.

String constraints

Feature	dottxt	OpenAI	Anthropic	Gemini
`minLength` / `maxLength`
`pattern` (regex)
`format`

Number constraints

Feature	dottxt	OpenAI	Anthropic	Gemini
`minimum` / `maximum`
`exclusiveMinimum` / `exclusiveMaximum`
`multipleOf`

Array constraints

Feature	dottxt	OpenAI	Anthropic	Gemini
`prefixItems` (tuples)
`minItems` / `maxItems`
`contains`
`uniqueItems`

Multiple choices

Feature	dottxt	OpenAI	Anthropic	Gemini
`enum`

Object constraints

Feature	dottxt	OpenAI	Anthropic	Gemini
Optional fields
`additionalProperties` (as schema)
`propertyNames`
`patternProperties`
Arbitrary JSON
`minProperties` / `maxProperties`

Composition

Feature	dottxt	OpenAI	Anthropic	Gemini
`anyOf`
`allOf`
`oneOf`
`not`

Conditionals

Feature	dottxt	OpenAI	Anthropic	Gemini
`if` / `then` / `else`
`dependentRequired`
`dependentSchemas`

Schema reuse and recursion

Feature	dottxt	OpenAI	Anthropic	Gemini
Recursive schemas

Schema limits

Limit	dottxt	OpenAI	Anthropic	Gemini
Nesting depth	None	10 levels	None documented	None documented
Total properties	None	5000	None documented	None documented
Enum values	None	1000	None documented	None documented
Optional parameters	None	N/A	24 per request	None documented
Union type parameters	None	N/A	16 per request	None documented

Handling of unsupported features

Provider	Behavior
dottxt	Rejects the schema with an error specifying the unsupported construct
OpenAI	With `strict: true`, unsupported schemas return an API error
Anthropic	SDK strips unsupported constraints, adds them as text in field descriptions, validates response client-side
Gemini	Silently ignores unsupported properties

String constraints

Number constraints

Array constraints

Multiple choices

Object constraints

Composition

Conditionals

Schema reuse and recursion

Schema limits

Handling of unsupported features

Sources

Next steps

​String constraints

​Number constraints

​Array constraints

​Multiple choices

​Object constraints

​Composition

​Conditionals

​Schema reuse and recursion

​Schema limits

​Handling of unsupported features

​Sources

​Next steps

String constraints

Number constraints

Array constraints

Multiple choices

Object constraints

Composition

Conditionals

Schema reuse and recursion

Schema limits

Handling of unsupported features

Sources

Next steps