> This page location: APIs & SDKs > CLI > Configuration commands > dev
> Full Neon documentation index: https://neon.com/docs/llms.txt

> Summary: The Neon CLI `neon dev` command runs Neon Functions locally with a dev server and hot reload. Pass --source to serve a single function entry module (optionally with --port for an explicit port), or omit --source to serve every function declared in neon.ts, each on its own dev server.

# Neon CLI command: dev

Run Neon Functions locally with a dev server

The `dev` command runs [Neon Functions](https://neon.com/docs/compute/functions/overview) locally with a dev server and hot reload. Serve one function from its entry module, or every function declared in your `neon.ts` policy.

## Usage

```bash
neon dev [--source <path>] [options]
```

## Options

| Option     | Description                                                                                                                                                                                                                                     | Type   | Default | Required |
| ---------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------ | ------- | :------: |
| `--env`    | Path to a .env file to load into the environment before evaluating neon.ts so Function env values resolve from it. Existing env vars are not overridden. Function env values that read process.env must be set in this file or the environment. | string | —       |    No    |
| `--port`   | Port to listen on (single-function mode only, with --source). Fails if taken. Without it (and without a PORT env var) a free port is chosen automatically.                                                                                      | number | —       |    No    |
| `--source` | Path to a single function entry module. Omit to serve every function declared in neon.ts.                                                                                                                                                       | string | —       |    No    |

## Examples

Serve one function on a free port with hot reload:

```bash
neon dev --source ./functions/hello.ts
```

Serve every function declared in `neon.ts` (one dev server each):

```bash
neon dev
```

Serve one function on an explicit port (fails if the port is taken):

```bash
neon dev --source ./functions/hello.ts --port 3000
```

## Environment variables

Before evaluating `neon.ts`, `neon dev` loads your project's `.env` and then `.env.local` into the environment. Values in `.env.local` override `.env`, and a variable already set in your shell wins over both. This lets function `env` values that read `process.env` resolve locally the same way they do for [`neon deploy --env`](https://neon.com/docs/cli/deploy). Pass `--env` to load only one file instead, resolved from the current directory:

```bash
neon dev --env .env.staging
```

Local functions inherit every loaded variable, including ones `neon.ts` doesn't declare. A deployed function only gets the variables `neon.ts` declares plus the ones Neon injects, so check that anything your code needs is declared before you deploy. The dev server's startup banner lists which env files it loaded and how many variables each one set.

`neon dev` never writes to these files. To reuse the branch credential behind the AI Gateway and Object Storage, it reads the file [`neon env pull`](https://neon.com/docs/cli/env) writes. Without that file, it resolves the credential again on every start, so run `neon env pull` once if you restart often.

## WebSockets

`neon dev` serves WebSocket upgrades locally, so you can test real-time functions before you deploy. Connect a client to the dev server's `ws://localhost:<port>` URL. See [WebSockets and SSE](https://neon.com/docs/compute/functions/websockets) for the function-side code.

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## Related docs (Configuration commands)

- [config](https://neon.com/docs/cli/config)
- [deploy](https://neon.com/docs/cli/deploy)
- [status](https://neon.com/docs/cli/status)

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