[Feature]: Logging details about incorrect requests

[ErykCh]

🚀 The feature, motivation and pitch

Hi,

when doing vibecoding sometimes AI prepares code to call API /chat/completions, which is not correct.

But this is not even a problem of my code. I am trying to run Google ADK library to use local model served by vLLM.

The problem I am encountering is that either I only get this information:
INFO: 10.147.81.70:62614 - "POST /v1/chat/completions HTTP/1.1" 400 Bad Request

if e.g. top_p=0 ​​has been set

or nothing appears in logs (like for Google ADK). And I know that the message reaches vLLM, because it did just moment ago, but I added something new like e.g. tool calling and it stops working and there is no information in logs.

Please provide a more detailed dump if the message cannot be parsed. Especially adding logging in the initial stages where an error occurs causes nothing to appear in the logs.

Alternatives

No response

Additional context

No response

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[ErykCh]

This is correct according to Google ADK message:

{
  "messages": [
    {
      "role": "system",
      "content": "Route user requests: Use Google Search agent for performing search, planning for travels like flights and hotels. Use tool calling for function calls. /no_think\n\nYou are an agent. Your internal name is \"RequestCoordinator\".\n\n The description about you is \"Main help desk router.\"\n\n\nYou have a list of other agents to transfer to:\n\n\nAgent name: Google_Search\nAgent description: Performs a Google search\n\n\nAgent name: Travel_Planning\nAgent description: Handles requests to Book flights, search hotels and book hotels\n\n\nIf you are the best to answer the question according to your description, you\ncan answer it.\n\nIf another agent is better for answering the question according to its\ndescription, call `transfer_to_agent` function to transfer the\nquestion to that agent. When transferring, do not generate any text other than\nthe function call.\n"
    },
    {
      "role": "user",
      "content": "What interesting things happened today?"
    }
  ],
  "model": "llm",
  "tools": [
    {
      "type": "function",
      "function": {
        "name": "transfer_to_agent",
        "description": "Transfer the question to another agent.\n\nThis tool hands off control to another agent when it's more suitable to\nanswer the user's question according to the agent's description.\n\nArgs:\n  agent_name: the agent name to transfer to.\n",
        "parameters": {
          "type": "object",
          "properties": {
            "agent_name": {
              "type": "string"
            }
          }
        }
      }
    }
  ]
}

vllm shows nothing in the logs, not even a bad request

[ErykCh]

it's because of the apostrophe used in the function description

        "description": "Transfer the question to another agent.\n\nThis tool hands off control to another agent when it's more suitable to\nanswer the user's question according to the agent's description.\n\nArgs:\n  agent_name: the agent name to transfer to.\n",

it's
user's
agent's

it's not my prompt, it's the function description built into Google ADK

[ErykCh]

These types of errors should be identified much faster

I had to write a proxy that logged everything between Google ADK and vLLM to find this problem

the problem with the apostrophe is probably not in vLLM itself but in the template for a given model

but I dare say that this type of problem should be identified right away