OpenAICompatibleToolMessage tool result should be an array #4890

wangfenjin · 2025-11-27T08:33:58Z

wangfenjin
Nov 27, 2025

tensorzero/tensorzero-core/src/endpoints/openai_compatible/types/chat_completions.rs

Lines 54 to 68 in 437ba75

    
           pub struct OpenAICompatibleAssistantMessage { 
        
               pub content: Option<Value>, 
        
               pub tool_calls: Option<Vec<OpenAICompatibleToolCall>>, 
        
           } 
        
           #[derive(Clone, Debug, Deserialize, PartialEq)] 
        
           #[serde(tag = "role")] 
        
           #[serde(rename_all = "lowercase")] 
        
           pub enum OpenAICompatibleMessage { 
        
               #[serde(alias = "developer")] 
        
               System(OpenAICompatibleSystemMessage), 
        
               User(OpenAICompatibleUserMessage), 
        
               Assistant(OpenAICompatibleAssistantMessage), 
        
               Tool(OpenAICompatibleToolMessage), 
        
           }

When LLM assistant requires multiple tool_use concurrently, it will require the following tool result also be an array, with the tool_call_id matches. Otherwise it will return error like:

"error": {

    "message": "An assistant message with 'tool_calls' must be followed by tool messages responding to each 'tool_call_id'. The following tool_call_ids did not have response messages: call_5lCYn0RkWOzv6sWEqhWAs0k1",

    "type": "invalid_request_error",

    "param": "messages.[5].role",

    "code": null

  }

Currently it's reproducible in gpt-5 and claude 4, grok seems ok with multiple tool sections

virajmehta · 2025-11-27T21:49:30Z

virajmehta
Nov 27, 2025
Maintainer

Hi @wangfenjin; can you send a way to reproduce the error you're seeing? We did not have great test coverage here so I opened a PR adding a test case but it passed without changes to production code with GPT-5-mini.

2 replies

wangfenjin Nov 28, 2025
Author

sorry I misunderstood the problem.

The real problem is one of the tool have image data, but tool_result can only be string, so I append the image_data as user message, and it's interleaved with the tool results. After append the tool results first it works now.

Thanks.

virajmehta Nov 28, 2025
Maintainer

Glad it's resolved!

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OpenAICompatibleToolMessage tool result should be an array #4890

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virajmehta Nov 27, 2025 Maintainer

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wangfenjin Nov 28, 2025 Author

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virajmehta Nov 28, 2025 Maintainer

wangfenjin
Nov 27, 2025

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virajmehta
Nov 27, 2025
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wangfenjin Nov 28, 2025
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virajmehta Nov 28, 2025
Maintainer