OpenAI-compatible providers fail with tools - missing 'type: object' in JSON Schema

[hughlv]

Bug Report: OpenAI-compatible providers fail with tools - missing "type": "object" in JSON Schema

Description

When using tools with OpenAI-compatible providers that strictly validate JSON schemas (like DeepSeek), all tool calls fail with the error:

Invalid schema for function 'functionName': schema must be a JSON Schema of 'type: "object"', got 'type: null'.

Root Cause

The bug is in the OpenAI-compatible provider used by DeepSeek. When converting tool schemas, the AI SDK creates JSON schemas without the required "type": "object" field.

Location in source code:

1. @ai-sdk/openai-compatible/dist/index.js line 239: Directly passes tool.inputSchema without validation
2. @ai-sdk/provider-utils/dist/index.js lines 1031-1033: Creates schema without type field:

jsonSchema({
  properties: {},
  additionalProperties: false
})

Reproduction

import { streamText } from 'ai';
import { deepseek } from '@ai-sdk/deepseek';
import { z } from 'zod';

const result = await streamText({
  model: deepseek('deepseek-chat'),
  messages: [{ role: 'user', content: 'What is the weather?' }],
  tools: {
    getWeather: {
      description: 'Get weather',
      parameters: z.object({
        location: z.string(),
      }),
      execute: async () => ({ weather: 'sunny' }),
    },
  },
});

What AI SDK sends (incorrect):

{
  "type": "function",
  "function": {
    "name": "getWeather",
    "description": "Get weather",
    "parameters": {
      "properties": {},
      "additionalProperties": false
    }
  }
}

What DeepSeek expects (correct):

{
  "type": "function",
  "function": {
    "name": "getWeather",
    "description": "Get weather",
    "parameters": {
      "type": "object",  // <-- This is missing!
      "properties": {
        "location": {
          "type": "string"
        }
      },
      "required": ["location"]
    }
  }
}

Verification

Direct API call to DeepSeek works fine with proper schema:

curl -X POST https://api.deepseek.com/v1/chat/completions \
  -H "Authorization: Bearer $DEEPSEEK_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "deepseek-chat",
    "messages": [{"role": "user", "content": "What is the weather?"}],
    "tools": [{
      "type": "function",
      "function": {
        "name": "getWeather",
        "parameters": {
          "type": "object",
          "properties": {"location": {"type": "string"}}
        }
      }
    }]
  }'

Proposed Fix

In @ai-sdk/provider-utils, the jsonSchema function should include "type": "object":

function jsonSchema(jsonSchema2, { validate } = {}) {
  // Ensure type: 'object' is set for object schemas
  if (jsonSchema2.properties && !jsonSchema2.type) {
    jsonSchema2.type = 'object';
  }
  // ... rest of function
}

Or in the asSchema function:

function asSchema(schema) {
  return schema == null ? jsonSchema({
    type: 'object',  // Add this line
    properties: {},
    additionalProperties: false
  }) : isSchema(schema) ? schema : zodSchema(schema);
}

Environment

• @ai-sdk/deepseek: 1.0.3
• @ai-sdk/openai-compatible: 1.0.3
• @ai-sdk/provider-utils: 3.0.1
• ai: 5.0.8

Impact

This bug prevents all tool usage with DeepSeek through the AI SDK, making it impossible to use function calling with this provider.

[lgrammel]

which zod version are you using? also can you import zod from zod/v3 or zod/v4?

[rodrimaia]

Also having the same issue. using latest zod@4.1.12. Just tested with zod/v3 and zod/v4 and still getting the same error.

Sorry, I just noticed I have to use inputSchema instead of parameters

[josuevalrob]

This shit is problematic, new deepseek is out there, and vercel has not update this?

Environment

• AI SDK version: 5.0.104
• @ai-sdk/deepseek: 1.0.31
• Node.js: 20.x
• Framework: Next.js 16.0.1

Issue

When using tool() with Zod schemas and DeepSeek provider, the generated JSON schema is missing "type": "object", causing DeepSeek API to reject all tool calls.

Error

Invalid schema for function 'search_material_content': schema must be a JSON Schema of 'type: "object"', got 'type: null'.

Reproduction

import { generateText, tool } from 'ai';
import { createDeepSeek } from '@ai-sdk/deepseek';
import { z } from 'zod';

const deepseek = createDeepSeek({ apiKey: process.env.DEEPSEEK_API_KEY });

const result = await generateText({
  model: deepseek('deepseek-chat'),
  prompt: 'Search for calcium information',
  tools: {
    search: tool({
      description: 'Search content',
      parameters: z.object({
        query: z.string(),
      }),
      execute: async ({ query }) => ({ results: [] }),
    }),
  },
});

Expected

JSON schema should include "type": "object" for tool parameters.

Actual

Schema is generated without "type": "object", DeepSeek API rejects it.

Workaround

Currently forced to use Ollama instead of DeepSeek, which has significantly worse tool-calling capabilities.

Impact

DeepSeek tool calling is completely broken with AI SDK. This blocks production use of DeepSeek for agentic workflows.

[bbb169]

It seems you can replace `parameters` with `inputSchema` and solve this problem @hughlv