> ## Documentation Index
> Fetch the complete documentation index at: https://ona.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Set up your first environment

> Create a Dev Container so your environments and agents have everything they need.

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.

## Create your first Dev Container

Create a `.devcontainer/devcontainer.json` file in your repository:

```json theme={null}
{
  "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.

## Run tasks on startup

For more control over startup behavior, use [Tasks & Services](/ona/configuration/tasks-and-services/overview):

```yaml theme={null}
# .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.

## Verify it works

Once your environment starts, verify the setup. These examples assume a Node.js project. Substitute your own project's commands:

```bash theme={null}
# 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.

## Next steps

* [Optimize startup times](/ona/configuration/devcontainer/optimizing-startup-times) with prebuilds and image caching
* [Dev Container reference](/ona/configuration/devcontainer/overview) for advanced configuration: multi-container setups, private images, elevated privileges
* [Teach agents your codebase](/ona/agents-md) so they understand your conventions