What is the difference between the tool() helper, DynamicTool, and StructuredTool class?

The tool() helper is a higher‑level factory that builds either a DynamicTool or DynamicStructuredTool for you. It's the recommended approach for most use cases because it automatically wires in newer runtime features such as state injection from LangGraph, context propagation, cancellation (AbortSignal), and streaming (runtime.writer).

DynamicStructuredTool is a concrete class that extends StructuredTool. It is designed for tools that accept structured data (multiple named arguments) validated against a Zod or JSON schema. You instantiate it directly with a configuration object containing name, description, schema, and func.

DynamicTool is a simpler class for tools that accept a single string input. It uses a default StringInputToolSchema and is useful for wrapping legacy APIs or functions that operate on a single query string.

For the LLM, both approaches look identical—they expose the same name, description, and argument schema. The differences are in developer ergonomics and runtime integration rather than what the model sees. The official recommendation for maintainable, future‑proof code is to standardize on the tool() helper for all new tools and gradually migrate existing DynamicStructuredTool usages to this pattern.