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homelab/raw/articles/opencode/docs/custom-tools.md

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+---
+type: agent-doc
+agent: OpenCode
+source: https://opencode.ai/docs/custom-tools/
+scraped: 2026-04-28T21:02:14.861865+00:00
+content_hash: 34c22729
+---
+# 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.
+
+```
+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>:
+
+```
+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:
+
+```
+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}`  },})
+```
+
+---
+
+### 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"
+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:
+
+```
+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: ${worktree}`  },})
+```
+
+Use context.directory for the session working directory. Use context.worktree for the git worktree root.
+
+---
+
+## Examples
+
+### Write a tool in Python
+
+You can write your tools in any language you want. Here’s an example that adds two numbers using Python.
+
+First, create the tool as a Python script:
+
+```
+import sys
+a = int(sys.argv[1])b = int(sys.argv[2])print(a + b)
+```
+
+Then create the tool definition that invokes it:
+
+```
+import { tool } from "@opencode-ai/plugin"import path from "path"
+export default tool({  description: "Add two numbers using Python",  args: {    a: tool.schema.number().describe("First number"),    b: tool.schema.number().describe("Second number"),  },  async execute(args, context) {    const script = path.join(context.worktree, ".opencode/tools/add.py")    const result = await Bun.$`python3 ${script} ${args.a} ${args.b}`.text()    return result.trim()  },})
+```
+
+Here we are using the Bun.$ utility to run the Python script.