Tool calls fail with 400 Bad Request due to strict JSON Schema violations (OpenAI)
The ADK framework's ChatCompletionsRequest serialization generates JSON payloads that violate strict OpenAI/Groq requirements. Specifically, it maps empty arguments maps and empty function response objects to null or omits them entirely, which causes the downstream API to drop the context and hallucinate.
Please make sure you read the contribution guide and file the issues in the right place.
Contribution guide.
🔴 Required Information
Describe the Bug:
When using third-party OpenAI-compatible providers like Groq, multi-turn tool calling fails. If an agent executes a tool that requires 0 arguments (like getCurrentTime), the ADK serializes the assistant's message with arguments: null or omits the arguments field. Furthermore, during tool declaration, it omits the parameters schema object entirely for zero-argument functions. Strict parsers (like Groq) reject or silently drop this malformed tool history, leading the model to lose context. Consequently, the model hallucinates raw XML-like tool calls, causing a fatal 400 Bad Request error. Additionally, JSON Schema enum types for tools are incorrectly serialized in uppercase (e.g., "STRING" instead of "string").
Steps to Reproduce:
- Configure an ADK agent with multiple tools (e.g.,
getCurrentTime, getWeather).
- Set the model provider to
groq/llama-3.3-70b-versatile.
- Send a prompt that requires executing a tool with no arguments.
- The first tool executes, but the subsequent request to the model crashes with a 400 Bad Request.
Expected Behavior:
The ADK ChatCompletionsRequest should strictly comply with the OpenAI JSON specifications:
arguments must be a non-null JSON string (e.g., "{}" if empty).content for tool roles must be a non-null string (e.g., "{}" if empty).parameters schema objects must exist in function declarations, even for zero-argument functions (e.g., {"type":"object", "properties":{}}).- JSON Schema
Type enums must be serialized in lowercase.
Observed Behavior:
The framework throws a 400 Bad Request exception due to model hallucinations caused by dropped context:
Exception in thread "main" java.lang.RuntimeException: java.io.IOException: HTTP request failed with status: Response{protocol=h2, code=400, message=, url=https://api.groq.com/openai/v1/chat/completions} - body: {"error":{"message":"tool call validation failed: attempted to call tool 'brave_search' which was not in request.tools","type":"invalid_request_error","code":"tool_use_failed","failed_generation":"<function=brave_search>{\"query\":\"HACK stock price\"}</function>"}}
Environment Details:
- ADK Library Version:
1.4.1-SNAPSHOT
- OS: Windows (also reproducible on macOS/Linux)
- TS Version: N/A
Model Information:
- Which model is being used:
groq/llama-3.3-70b-versatile
🟡 Optional Information
How often has this issue occurred?:
Tool calls fail with 400 Bad Request due to strict JSON Schema violations (OpenAI)
The ADK framework's
ChatCompletionsRequestserialization generates JSON payloads that violate strict OpenAI/Groq requirements. Specifically, it maps emptyargumentsmaps and empty functionresponseobjects tonullor omits them entirely, which causes the downstream API to drop the context and hallucinate.Please make sure you read the contribution guide and file the issues in the right place.
Contribution guide.
🔴 Required Information
Describe the Bug:
When using third-party OpenAI-compatible providers like Groq, multi-turn tool calling fails. If an agent executes a tool that requires 0 arguments (like
getCurrentTime), the ADK serializes the assistant's message witharguments: nullor omits the arguments field. Furthermore, during tool declaration, it omits theparametersschema object entirely for zero-argument functions. Strict parsers (like Groq) reject or silently drop this malformed tool history, leading the model to lose context. Consequently, the model hallucinates raw XML-like tool calls, causing a fatal 400 Bad Request error. Additionally, JSON Schema enum types for tools are incorrectly serialized in uppercase (e.g.,"STRING"instead of"string").Steps to Reproduce:
getCurrentTime,getWeather).groq/llama-3.3-70b-versatile.Expected Behavior:
The ADK
ChatCompletionsRequestshould strictly comply with the OpenAI JSON specifications:argumentsmust be a non-null JSON string (e.g.,"{}"if empty).contentfor tool roles must be a non-null string (e.g.,"{}"if empty).parametersschema objects must exist in function declarations, even for zero-argument functions (e.g.,{"type":"object", "properties":{}}).Typeenums must be serialized in lowercase.Observed Behavior:
The framework throws a 400 Bad Request exception due to model hallucinations caused by dropped context:
Environment Details:
1.4.1-SNAPSHOTModel Information:
groq/llama-3.3-70b-versatile🟡 Optional Information
How often has this issue occurred?: