SDK

tip

The SDK is the foundation for building custom tools, plugins, and programmatic agents.

Installation

npm install opencode-ai
# or
yarn add opencode-ai
# or
pnpm add opencode-ai

Custom Tools

Custom tools allow you to define project-specific functions that the AI agent can invoke. Tools are registered in your OpenCode configuration and implemented as JavaScript/TypeScript modules.

import { tool } from 'opencode-ai/sdk';

export const weatherTool = tool({
  name: 'get_weather',
  description: 'Get the current weather for a location',
  parameters: {
    type: 'object',
    properties: {
      location: {
        type: 'string',
        description: 'City and state or country'
      }
    },
    required: ['location']
  },
  execute: async ({ location }) => {
    const response = await fetch(
      `https://api.weather.example/v1/current?q=${encodeURIComponent(location)}`
    );
    return response.json();
  }
});

Register custom tools in your project configuration:

{
  "tool": ["./tools/weather.mjs"]
}

Each tool file should export an array of tool definitions or a single tool definition. Tools receive structured arguments and return results that the agent can interpret.

Plugins

Plugins extend OpenCode with hooks, custom tools, middleware, and lifecycle callbacks. The SDK exports a plugin API for building and publishing plugins.

import { definePlugin } from 'opencode-ai/sdk';

export default definePlugin({
  name: 'my-custom-plugin',
  version: '1.0.0',
  hooks: {
    'tool.execute.before': async ({ tool, args }) => {
      console.log(`Executing tool: ${tool.name}`, args);
    },
    'tool.execute.after': async ({ tool, result }) => {
      console.log(`Tool ${tool.name} completed`, result);
    }
  },
  tools: [myCustomTool]
});

See the Plugins page for detailed plugin authoring guidance.

Tool Execution Hooks

The SDK exposes lifecycle hooks that fire before and after tool execution. These hooks are useful for logging, auditing, transforming arguments, or modifying results.

{
  hooks: {
    'tool.execute.before': async ({ tool, args, session }) => {
      // Validate or transform arguments before execution
      return args;
    },
    'tool.execute.after': async ({ tool, args, result, session }) => {
      // Log results, send telemetry, or transform output
      return result;
    }
  }
}

Hooks can be async and may optionally return modified data. If a before hook throws, the tool execution is aborted.

Session Management API

The SDK provides APIs to manage sessions programmatically, useful for building custom frontends or automation scripts.

import { SessionManager } from 'opencode-ai/sdk';

const manager = new SessionManager();

// Create a new session
const session = await manager.create({
  agent: 'build',
  model: 'anthropic/claude-sonnet-4'
});

// Send a message
const response = await session.send('Explain how dependency injection works');

// Stream response
for await (const chunk of session.sendStream('Write a React component')) {
  process.stdout.write(chunk.text);
}

// List all sessions
const sessions = await manager.list();

// Resume a session
const resumed = await manager.resume(sessionId);

Provider Integration API

Register custom LLM providers through the SDK. This is useful for connecting internal model endpoints or proprietary APIs.

import { defineProvider } from 'opencode-ai/sdk';

export const myProvider = defineProvider({
  id: 'my-corp',
  name: 'My Corp Models',
  models: async () => {
    const res = await fetch('https://api.my-corp.example/models');
    return res.json();
  },
  complete: async ({ model, messages, options }) => {
    const res = await fetch('https://api.my-corp.example/chat', {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'Authorization': `Bearer ${options.apiKey}`
      },
      body: JSON.stringify({ model, messages, ...options })
    });
    return res.json();
  },
  stream: async function* ({ model, messages, options }) {
    const res = await fetch('https://api.my-corp.example/chat', {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'Authorization': `Bearer ${options.apiKey}`
      },
      body: JSON.stringify({ model, messages, stream: true, ...options })
    });
    const reader = res.body.getReader();
    while (true) {
      const { done, value } = await reader.read();
      if (done) break;
      yield JSON.parse(new TextDecoder().decode(value));
    }
  }
});

Agent Creation API

Define and configure agents programmatically. This is useful for creating specialized assistants that can be invoked from your own application.

import { defineAgent } from 'opencode-ai/sdk';

const codeReviewAgent = defineAgent({
  name: 'code-reviewer',
  mode: 'plan',
  model: 'anthropic/claude-sonnet-4',
  system: 'You are a senior engineer reviewing code changes. Focus on security, performance, and maintainability.',
  tools: ['read_file', 'search_files', 'run_command'],
  temperature: 0.2,
  maxSteps: 20
});

// Use the agent programmatically
const review = await codeReviewAgent.run({
  task: 'Review the changes in src/components/Button.tsx',
  context: { repo: 'my-project', branch: 'feature/button-fix' }
});

tip

Browse the npm package for the complete TypeScript type definitions and API surface.

SDK Reference

The full SDK is exported from the opencode-ai package:

import {
  tool,
  definePlugin,
  defineProvider,
  defineAgent,
  SessionManager,
  ToolExecutionContext,
  HookRegistry,
  type Tool,
  type Plugin,
  type Provider,
  type Agent,
  type Session,
  type Message,
  type ToolResult
} from 'opencode-ai/sdk';

Refer to the npm package documentation for the complete API surface and TypeScript type definitions.

Patterns and Best Practices