A StateWeave tool is a small object with a name, description, schema, and executor. 
import { z } from "zod";
import type { Tool } from "stateweave";

const readFileTool: Tool = {
  name: "read_file",
  description: "Read a source file by path.",
  schema: z.object({ path: z.string() }),
  async execute(args) {
    const { path } = z.object({ path: z.string() }).parse(args);
    return await readFile(path, "utf8");
  }
};
Pass tools to the agent. 
const agent = new StateWeaveAgent({
  model,
  tools: [readFileTool],
  maxSteps: 5
});
When the model emits a tool operation: 
{
  "op": "call_tool",
  "tool": "read_file",
  "args": { "path": "auth.ts" }
}
StateWeave validates the args, executes the tool, and inserts the result as a tool_result node. 
tool_call -> tool_result -> next GraphFrame
The next model step sees the tool result as graph state, not as an opaque transcript line.