AI

Invalid schema for function: schema must be a JSON Schema of 'type: "object"'

Issue

When using tools, generateObject, or streamObject with Zod schemas, you encounter this error:

Error [AI_APICallError]: Invalid schema for function 'json': schema must be a JSON Schema of 'type: "object"', got 'type: "string"'.

or similar variants like:

  • got 'type: "Null"
  • Invalid schema for function 'calculator'
  • Invalid schema for function '[your-function-name]'

This error occurs when using:

  • Tool definitions with tool() function
  • Structured object generation with generateObject() or streamObject()
  • Any AI SDK feature that converts Zod schemas to JSON schemas

Cause

The AI SDK v4 is not compatible with Zod v4. The schema conversion process that transforms Zod schemas into JSON schemas breaks with Zod v4's internal structure changes.

Solution 

npm install zod@3.25.76

or with pnpm:

pnpm add zod@3.25.76

Option 2: Upgrade to AI SDK v5 (Beta)

If you need Zod v4, you can upgrade to the beta version of AI SDK v5:

# replace openai and react with your provider and framework of choice
npm install ai@beta @ai-sdk/openai@beta @ai-sdk/react@beta

Note: v5 is currently in beta and may have breaking changes. See the v5 migration guide.

Additional Resources