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Add a Dev Container to your repository so every environment, whether started by a teammate or an agent, launches with the right runtimes, tools, and services already running.
  • Agents get a reproducible environment to execute commands, run tests, and iterate
  • New team members start an environment and immediately have everything they need
  • Everyone works in the same setup, no more “it works on my machine”
A Dev Container can include language runtimes, databases, tools, editor extensions, environment variables, and startup tasks.

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Create your first Dev Container

Create a .devcontainer/devcontainer.json file in your repository: 
{
  "name": "My Project",
  "image": "mcr.microsoft.com/devcontainers/javascript-node:20",
  "features": {
    "ghcr.io/devcontainers/features/docker-in-docker:2": { "moby": false }
  },
  "customizations": {
    "vscode": {
      "extensions": [
        "dbaeumer.vscode-eslint",
        "esbenp.prettier-vscode"
      ]
    }
  },
  "postCreateCommand": "npm install"
}
This gives you:
  • Node.js 20 with npm
  • Docker available inside the environment
  • ESLint and Prettier extensions
  • Dependencies installed automatically
Start an environment from your repository. Ona builds the container and you’re ready to code.

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Run tasks on startup

For more control over startup behavior, use Tasks & Services: 
# .ona/automations.yaml
tasks:
  install:
    name: Install dependencies
    command: npm install
    triggeredBy:
      - postDevcontainerStart

services:
  database:
    name: PostgreSQL
    commands:
      start: docker run --rm -t --name database -p 5432:5432 -e POSTGRES_PASSWORD=postgres postgres:15
      ready: docker exec database pg_isready
      stop: docker stop database
    triggeredBy:
      - postEnvironmentStart
Now every environment starts with dependencies installed and a database running.

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Verify it works

Once your environment starts, verify the setup. These examples assume a Node.js project. Substitute your own project’s commands: 
# Check your runtime
node --version

# Run your tests (if your project has a test script)
npm test

# Start your dev server (if your project has a dev script)
npm run dev
If your project’s commands work inside the environment, your Dev Container is ready. Agents will be able to run the same commands reliably.

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Next steps