Writing OpenCode Plugins

Project structure

Use the shim pattern to separate development from plugin loading:

plugin-name/
├── src/
│   └── main.ts              # Main implementation
├── .opencode/
│   ├── package.json         # Plugin dependencies
│   └── plugins/
│       └── shim.ts         # Loads plugin from src/
├── test/
│   ├── unit.test.ts        # Unit tests
│   └── e2e.test.ts        # E2E tests
├── package.json            # Root package.json
└── tsconfig.json           # TypeScript config

Shim file (.opencode/plugins/*.ts)

The shim file is loaded by OpenCode and re-exports from src:

export { PluginName as PluginNamePlugin } from "../../src/main"

Benefits:

• ✅ Development with TypeScript and type safety
• ✅ Easy unit/integration testing
• ✅ Source code not duplicated in .opencode/

Plugin structure

A plugin exports a function that receives context and returns hooks:

export const MyPlugin: Plugin = async ({ directory, worktree, project, client, $ }) => {
  return {
    "shell.env": async (input, output) => {
      // input.cwd - current working directory
      // output.env - modify shell environment
    },
  }
}

Context parameters

• directory

  - Current working directory

• worktree

  - Git worktree path

• project

  - Project information

• client

  - OpenCode SDK client

• $

  - Bun shell API

Available hooks

Common hooks:

• shell.env

  - Inject environment variables before shell execution

• tool.execute.before

  - Intercept tool calls before execution

• tool.execute.after

  - Post-process tool results

• file.edited

  - React to file changes

Testing strategy

Unit tests

Test core logic in isolation using

bun test

:

// test/unit.test.ts
import { test, expect, describe, beforeEach, afterEach } from "bun:test"
import { coreFunction } from "../src/main"
import { tmpdir } from "os"
import { join } from "path"
import { mkdir, writeFile, rm } from "fs/promises"

describe("coreFunction", () => {
  let testDir: string

  beforeEach(async () => {
    testDir = join(tmpdir(), `test-${Date.now()}`)
    await mkdir(testDir, { recursive: true })
  })

  afterEach(async () => {
    await rm(testDir, { recursive: true, force: true })
  })

  test("handles basic case", async () => {
    const result = await coreFunction(testDir)
    expect(result).toBeDefined()
  })
})

E2E tests

Test full plugin integration with OpenCode CLI:

// test/e2e.test.ts
import { test, expect, describe, beforeEach, afterEach } from "bun:test"
import { $ } from "bun"

describe("E2E", () => {
  test("plugin works with OpenCode CLI", async () => {
    try {
      const result = await $`opencode run 'test command'`.quiet()
      expect(result.exitCode).toBe(0)
      expect(result.stdout).toContain("expected")
    } catch (error) {
      if (error instanceof Error && error.message.includes("ENOENT")) {
        console.log("Skipping: opencode CLI not found")
        return
      }
      throw error
    }
  }, { timeout: 30_000 })
})

Test fixtures

Committed test data in

test/fixtures/

:

test/fixtures/
├── basic/           # Basic scenarios
├── advanced/        # Complex scenarios
└── e2e/           # E2E test workspace

Test fixtures can contain safe-to-commit test data, encryption keys, etc.

Dependencies

Root package.json

Contains dev dependencies and publishing info:

{
  "name": "@scope/plugin-name",
  "version": "0.1.0",
  "main": "./src/main.ts",
  "type": "module",
  "exports": {
    ".": {
      "types": "./src/main.ts",
      "import": "./src/main.ts"
    }
  },
  "scripts": {
    "test": "bun test",
    "test:unit": "bun test test/unit.test.ts",
    "test:e2e": "bun test test/e2e.test.ts"
  },
  "dependencies": {
    "@opencode-ai/plugin": "1.2.10"
  },
  "publishConfig": {
    "access": "public"
  }
}

.opencode/package.json

Plugin runtime dependencies only:

{
  "name": "plugin-name-runtime",
  "private": true,
  "dependencies": {
    "@opencode-ai/plugin": "1.2.10"
  }
}

OpenCode automatically runs

bun install

in

.opencode/

at startup.

Publishing

Using np (recommended)

# Install dependencies
bun install

# Login to npm
npm login

# Publish with version prompt
bunx np --any-branch

Manual publish

# Bump version
npm version patch  # or minor, or major

# Publish to npm
npm publish --access public

.npmignore

Exclude development files from npm package:

# Testing
test/
coverage/

# OpenCode plugin (local use)
.opencode/
.opencode.json

# Development notes
notes/
AGENTS.md

# Serena
.serena/

# GitHub CI
.github/

# Build/cache
node_modules/
dist/
out/
*.tsbuildinfo
.cache/
.eslintcache

# Logs
logs/
*.log

# Environment files
.env
.env.*
.env.keys
.env.*.keys

# macOS
.DS_Store

# IDE
.idea/
*.swp
*.swo

# npm
bun.lock

TypeScript configuration

Use strict TypeScript with Bun defaults:

{
  "compilerOptions": {
    "lib": ["ESNext"],
    "target": "ESNext",
    "module": "Preserve",
    "moduleDetection": "force",
    "jsx": "react-jsx",
    "allowJs": true,
    "moduleResolution": "bundler",
    "allowImportingTsExtensions": true,
    "verbatimModuleSyntax": true,
    "noEmit": true,
    "strict": true,
    "skipLibCheck": true,
    "noFallthroughCasesInSwitch": true,
    "noUncheckedIndexedAccess": true,
    "noImplicitOverride": true,
    "noUnusedLocals": false,
    "noUnusedParameters": false,
    "noPropertyAccessFromIndexSignature": false
  }
}

AGENTS.md (Bun instructions)

Include Bun-specific guidance in AGENTS.md:

---
description: Use Bun instead of Node.js, npm, pnpm, or vite.
globs: "*.ts, *.tsx, *.html, *.css, *.js, *.jsx, package.json"
alwaysApply: false
---

Default to using Bun instead of Node.js.

- Use `bun <file>` instead of `node <file>` or `ts-node <file>`
- Use `bun test` instead of `jest` or `vitest`
- Use `bun install` instead of `npm install`
- Use `bunx <package> <command>` instead of `npx <package> <command>`

Development workflow

1. Edit

   src/main.ts

   - main implementation
2. Run tests:

   bun test

3. Shim in

   .opencode/plugins/*.ts

   auto-reloads on OpenCode restart

Plugin installation

Project-level (development)

Plugin files in

.opencode/plugins/

auto-load on OpenCode restart.

Global (all projects)

mkdir -p ~/.config/opencode/plugins
cp .opencode/plugins/*.ts ~/.config/opencode/plugins/
cp .opencode/package.json ~/.config/opencode/package.json

From npm (users)

Add to

opencode.json

:

{
  "$schema": "https://opencode.ai/config.json",
  "plugin": ["@scope/plugin-name"]
}

OpenCode auto-installs npm packages to

~/.cache/opencode/node_modules/

.

Best practices

Extract testable functions

Separate core logic from hooks:

// Bad: Logic inside hook
export const Plugin = async () => ({
  "shell.env": async (input, output) => {
    // All logic here...
  }
})

// Good: Extracted function
async function coreLogic(path: string): Promise<Record<string, string>> {
  // Pure logic, easy to test
}

export const Plugin = async () => ({
  "shell.env": async (input, output) => {
    const result = await coreLogic(input.cwd)
    Object.assign(output.env, result)
  }
})

Error handling

Use try/catch with meaningful errors:

try {
  const result = await riskyOperation()
  return result
} catch (error) {
  console.error("Operation failed:", error)
  throw new Error(`Failed to process: ${error}`)
}

Async hooks

All hooks are async - use async/await:

export const Plugin = async () => ({
  "shell.env": async (input, output) => {
    const data = await loadData()
    output.env.VAR = data.value
  }
})

Non-mutating output

Check before setting:

if (!(key in output.env)) {
  output.env[key] = value
}

Quiet mode

Suppress console output for clean logs:

someLibrary.configure({ quiet: true })

CI/CD

Example GitHub Actions:

name: CI

on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: oven-sh/setup-bun@v2
        with:
          bun-version: latest
      - run: bun install
      - run: bun test

References

• OpenCode Plugins Documentation
• OpenCode SDK Documentation
• Bun Documentation