vercel/ai · error · InvalidArgumentError

Invalid argument for parameter schema: Schema is not support

Error message

Invalid argument for parameter schema: Schema is not supported for no-schema output.

What it means

generateObject/streamObject validate input consistency before calling a provider. When you pass output: 'no-schema' (or Output.noSchema()), the model returns free-form text with no structured constraints, so a schema contradicts the requested mode. The library throws InvalidArgumentError to fail fast rather than silently ignoring the schema.

Source

Thrown at packages/ai/src/generate-object/validate-object-generation-input.ts:33

  enumValues?: Array<unknown>;
}) {
  if (
    output != null &&
    output !== 'object' &&
    output !== 'array' &&
    output !== 'enum' &&
    output !== 'no-schema'
  ) {
    throw new InvalidArgumentError({
      parameter: 'output',
      value: output,
      message: 'Invalid output type.',
    });
  }

  if (output === 'no-schema') {
    if (schema != null) {
      throw new InvalidArgumentError({
        parameter: 'schema',
        value: schema,
        message: 'Schema is not supported for no-schema output.',
      });
    }

    if (schemaDescription != null) {
      throw new InvalidArgumentError({
        parameter: 'schemaDescription',
        value: schemaDescription,
        message: 'Schema description is not supported for no-schema output.',
      });
    }

    if (schemaName != null) {
      throw new InvalidArgumentError({
        parameter: 'schemaName',
        value: schemaName,

View on GitHub (pinned to 69428b1f8b)

Solutions

Remove the schema property from the generateObject/streamObject call when using output: 'no-schema'.
If you actually want structured output, change output to 'object' (default) and keep the schema.
If you only need a description for the model, move the guidance into the prompt instead of schema/schemaDescription.

Example fix

// before
generateObject({ model, output: 'no-schema', schema: z.object({ name: z.string() }), prompt });
// after
generateObject({ model, output: 'no-schema', prompt });

Defensive patterns

Strategy: validation

Validate before calling

function assertNoSchemaOptions(opts) {
  if (opts.output === 'no-schema' && opts.schema != null) {
    throw new Error("schema must be omitted when output is 'no-schema'");
  }
}

Type guard

function isNoSchemaOptions(opts) {
  return opts.output === 'no-schema' && opts.schema == null;
}

Try / catch

try {
  await generateObject({ model, output: 'no-schema', prompt });
} catch (error) {
  if (InvalidArgumentError.isInstance(error) && error.parameter === 'schema') {
    // re-call without schema
  }
  throw error;
}

Prevention

Build call options conditionally: only include schema for 'object'/'array' output.
Avoid spreading shared option objects into generateObject calls.
Rely on TypeScript overloads so no-schema calls are not accepted with schema.

When it happens

Trigger: Calling generateObject({ model, output: 'no-schema', schema: someZodSchema, prompt }) or the same with streamObject, or passing schema alongside Output.noSchema(). Any non-null schema value (including an empty object schema) triggers it.

Common situations: Refactoring a previously schema-based call to no-schema output but leaving the old schema option in place; spreading a shared options object that contains schema; switching from generateText to generateObject for unrestricted output while keeping schema.

Related errors

AI-assisted analysis of vercel/ai@69428b1f8b (2026-08-30). Data as JSON: /api/errors/4dfb3325798f80e9. Report an issue: GitHub.