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---
title: Custom Tools
description: Create tools the LLM can call in opencode.
---
Custom tools are functions you create that the LLM can call during conversations. They work alongside opencode's [built-in tools](/docs/tools) like `read`, `write`, and `bash`.
---
## Creating a tool
Tools are defined as **TypeScript** or **JavaScript** files. However, the tool definition can invoke scripts written in **any language** — TypeScript or JavaScript is only used for the tool definition itself.
---
### Location
They can be defined:
- Locally by placing them in the `.opencode/tools/` directory of your project.
- Or globally, by placing them in `~/.config/opencode/tools/`.
---
### Structure
The easiest way to create tools is using the `tool()` helper which provides type-safety and validation.
```ts title=".opencode/tools/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.
---
#### 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/tools/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`.
---
#### Name collisions with built-in tools
Custom tools are keyed by tool name. If a custom tool uses the same name as a built-in tool, the custom tool takes precedence.
For example, this file replaces the built-in `bash` tool:
```ts title=".opencode/tools/bash.ts"
import { tool } from "@opencode-ai/plugin"
export default tool({
description: "Restricted bash wrapper",
args: {
command: tool.schema.string(),
},
async execute(args) {
return `blocked: ${args.command}`
},
})
```
:::note
Prefer unique names unless you intentionally want to replace a built-in tool. If you want to disable a built in tool but not override it, use [permissions](/docs/permissions).
:::
---
### 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/tools/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, directory, worktree } = context
return `Agent: ${agent}, Session: ${sessionID}, Message: ${messageID}, Directory: ${directory}, Worktree: ${worktree}`
},
})
```
Use `context.directory` for the session working directory.
Use `context.worktree` for the git worktree root.
---
## Examples
### Write a tool in Python
You can write your tools in any language you want. Here's an example that adds two numbers using Python.
First, create the tool as a Python script:
```python title=".opencode/tools/add.py"
import sys
a = int(sys.argv[1])
b = int(sys.argv[2])
print(a + b)
```
Then create the tool definition that invokes it:
```ts title=".opencode/tools/python-add.ts" {10}
import { tool } from "@opencode-ai/plugin"
import path from "path"
export default tool({
description: "Add two numbers using Python",
args: {
a: tool.schema.number().describe("First number"),
b: tool.schema.number().describe("Second number"),
},
async execute(args, context) {
const script = path.join(context.worktree, ".opencode/tools/add.py")
const result = await Bun.$`python3 ${script} ${args.a} ${args.b}`.text()
return result.trim()
},
})
```
Here we are using the [`Bun.$`](https://bun.com/docs/runtime/shell) utility to run the Python script.
|
