Custom Tools

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 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.

.opencode/tools/database.ts

import { tool } from"@opencode-ai/plugin"
exportdefaulttool({
description: "Query the project database",
args: {
query: tool.schema.string().describe("SQL query to execute"),
},
asyncexecute(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>:

.opencode/tools/math.ts

import { tool } from"@opencode-ai/plugin"
exportconstadd=tool({
description: "Add two numbers",
args: {
a: tool.schema.number().describe("First number"),
b: tool.schema.number().describe("Second number"),
},
asyncexecute(args) {
return (args.a + args.b).toString()
},
})
exportconstmultiply=tool({
description: "Multiply two numbers",
args: {
a: tool.schema.number().describe("First number"),
b: tool.schema.number().describe("Second number"),
},
asyncexecute(args) {
return (args.a * args.b).toString()
},
})

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:

.opencode/tools/bash.ts

import { tool } from"@opencode-ai/plugin"
exportdefaulttool({
description: "Restricted bash wrapper",
args: {
command: tool.schema.string(),
},
asyncexecute(args) {
return`blocked: ${args.command}`
},
})

Arguments

You can use tool.schema, which is just Zod, to define argument types.

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

You can also import Zod directly and return a plain object:

import { z } from"zod"
exportdefault {
description: "Tool description",
args: {
param: z.string().describe("Parameter description"),
},
asyncexecute(args, context) {
// Tool implementation
return"result"
},
}

Context

Tools receive context about the current session:

.opencode/tools/project.ts

import { tool } from"@opencode-ai/plugin"
exportdefaulttool({
description: "Get project information",
args: {},
asyncexecute(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:

.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:

.opencode/tools/python-add.ts

import { tool } from"@opencode-ai/plugin"
import path from"path"
exportdefaulttool({
description: "Add two numbers using Python",
args: {
a: tool.schema.number().describe("First number"),
b: tool.schema.number().describe("Second number"),
},
asyncexecute(args, context) {
constscript= path.join(context.worktree, ".opencode/tools/add.py")
constresult=await Bun.$`python3 ${script} ${args.a} ${args.b}`.text()
return result.trim()
},
})

Here we are using the Bun.$ utility to run the Python script.

URL: https://opencode.ai/docs/custom-tools

⇱ Custom Tools | OpenCode