Agent Frameworks Compared: Tool-Calling Schema Handling

You build an agent with working tool calling, then change the model behind it and the tool calls start failing. Your tool definition did not change. The request and response format the model expects did, because each provider uses its own shape for tool definitions, tool call responses, argument encoding, and tool results. If nothing in your stack translates between those shapes, a model swap turns into new parsing code and new failure modes. This article compares how six agent frameworks define tool schemas and translate them across providers, and where the translation runs in each case. It then shows how we normalize tool calling at the API layer so the shape your application sends and receives stays the same for every tool-capable model on OpenRouter. OpenAI, Anthropic, and Google each define tools and return tool calls with a different wire format. A tool definition written for one does not work unchanged on another. LangChain and LangGraph translate one tool definition per provider. CrewAI delegates translation to the client it routes to. The OpenAI Agents SDK, the Claude Agent SDK, and Google ADK are built around one provider’s format. Microsoft Agent Framework delegates to the configured model connector. OpenRouter accepts…