Custom tools are functions you create that the LLM can call during conversations. They work alongside opencode's built-in tools like `read`, `write`, and `bash`.

---

## Creating a tool

Tools are defined as **TypeScript** or **JavaScript** files.

---

### Location

They can defined:

- Locally by placing them in the `.opencode/tool/` directory of your project.
- Or globally, by placing them in `~/.config/opencode/tool/`.

---

### Structure

The easiest way to create tools is using the `tool()` helper which provides type-safety and validation.

```ts title=".opencode/tool/database.ts" {1}
import { tool } from "@opencode-ai/plugin";

export default tool({
	description: "Query the project database",
	args: {
		query: tool.schema.string().describe("SQL query to execute"),
	},
	async execute(args) {
		// Your database logic here
		return `Executed query: ${args.query}`;
	},
});
```

The **filename** becomes the **tool name**. The above creates a `database` tool.

---

### Arguments

You can use `tool.schema`, which is just [Zod](https://zod.dev), to define argument types.

```ts "tool.schema"
args: {
	query: tool.schema.string().describe("SQL query to execute");
}
```

You can also import [Zod](https://zod.dev) directly and return a plain object:

```ts {6}
import { z } from "zod";

export default {
	description: "Tool description",
	args: {
		param: z.string().describe("Parameter description"),
	},
	async execute(args, context) {
		// Tool implementation
		return "result";
	},
};
```

---

## Context

Tools receive context about the current session:

```ts title=".opencode/tool/project.ts" {8}
import { tool } from "@opencode-ai/plugin";

export default tool({
	description: "Get project information",
	args: {},
	async execute(args, context) {
		// Access context information
		const { agent, sessionID, messageID } = context;
		return `Agent: ${agent}, Session: ${sessionID}, Message: ${messageID}`;
	},
});
```

---

## Multiple tools per file

You can also export multiple tools from a single file. Each export becomes **a separate tool** with the name **`<filename>_<exportname>`**:

```ts title=".opencode/tool/math.ts"
import { tool } from "@opencode-ai/plugin";

export const add = tool({
	description: "Add two numbers",
	args: {
		a: tool.schema.number().describe("First number"),
		b: tool.schema.number().describe("Second number"),
	},
	async execute(args) {
		return args.a + args.b;
	},
});

export const multiply = tool({
	description: "Multiply two numbers",
	args: {
		a: tool.schema.number().describe("First number"),
		b: tool.schema.number().describe("Second number"),
	},
	async execute(args) {
		return args.a * args.b;
	},
});
```

This creates two tools: `math_add` and `math_multiply`.