Tools: Give Your Agent Hands

What it is#

Tools are typed functions the model can call. Drop a TypeScript file in tools/ and Eve discovers it; the filename becomes the tool name.

Why you'd care#

This is how an agent does things — fetch live data, hit an API, compute a result. No manual registration; the filesystem is the interface.

Before#

The agent can only talk. Ask for the weather and it guesses.

After#

import { defineTool } from "eve/tools";
import { z } from "zod";

export default defineTool({
  description: "Get the current weather for a city.",
  inputSchema: z.object({ cityName: z.string() }),
  async execute(input) {
    const res = await fetch(
      `${process.env.WEATHER_API_URL}/current?city=${input.cityName}`
    );
    const data = await res.json();
    return data.current_condition[0];
  },
});

Name the file get_weather.ts and the tool is get_weather. The Zod inputSchema types the arguments the model must provide.

Do it yourself#

1. Create agent/tools/get_weather.ts with the code above.
2. Run eve dev and ask "What's the weather in Lisbon?"
3. Confirm the model called the tool and returned typed data.
4. Add a second tool (e.g. a calculator) and call it.

Gotchas#

• The inputSchema (Zod) is what the model sees — make descriptions precise.
• The return value is what the model receives back; shape it for clarity.

Recap#

tools/ turns a talking agent into a doing agent. Filename = tool name, Zod = typed input. Next, reusable playbooks via skills.