additionalProperties: false
A keyword in JSON Schema that controls additional fields. When set to false, it prohibits fields not declared in properties, making validation strict.
Core Facts
Timeline (last 90 days)
Tool interfaces should use JSON schema with additionalProperties: false, and also register risk, timeout, retry, idempotency and approval requirements.
The validation strategy uses additionalProperties: false plus an explicit required list, which can precisely distinguish whether the model output a field outside the Schema or is missing a required field.
The core change in @ai-sdk/xai 4.0.59 is a fix for the xAI provider failing to correctly preserve the additionalProperties: false constraint field when generating tool definitions.
Many providers (including OpenAI) explicitly require that tool definitions carry the additionalProperties: false field in order to enable strict-mode structured output.
All Facts (5)
Setting additionalProperties: false in a JSON Schema rejects any extra fields not explicitly declared in the schema, eliminating the possibility of the model inventing additional fields.
80%UnverifiedTool interfaces should use JSON schema with additionalProperties: false, and also register risk, timeout, retry, idempotency and approval requirements.
50%UnverifiedThe validation strategy uses additionalProperties: false plus an explicit required list, which can precisely distinguish whether the model output a field outside the Schema or is missing a required field.
50%UnverifiedThe core change in @ai-sdk/xai 4.0.59 is a fix for the xAI provider failing to correctly preserve the additionalProperties: false constraint field when generating tool definitions.
50%UnverifiedMany providers (including OpenAI) explicitly require that tool definitions carry the additionalProperties: false field in order to enable strict-mode structured output.
50%