# atmos.lsp

The `atmos.lsp` function runs `atmos lsp` through the current Atmos executable. Its one subcommand starts the
Atmos Language Server Protocol server used for editor integration.

## Usage

```python
atmos.lsp(
    *positionals,
    flags = {},
    args = [],
    working_directory = ...,
    env = ...,
    output = "stream",
    check = True,
)
```

## Subcommands

Pass the subcommand as a string before the keyword arguments. The call `atmos.lsp("start")` runs `atmos lsp start`.

| Subcommand | Purpose |
| --- | --- |
| [`start`](/cli/commands/lsp/start) | Start the Atmos LSP server. |

See the [`atmos lsp start` command reference](/cli/commands/lsp/start) for details.

## Arguments

- **`*positionals`**

  (Optional) Strings placed on the command line right after `lsp`, in order: the subcommand. Every value must
  be a string.
- **`flags`**

  (Optional) A dictionary of command-line options; see
  [flag translation](/functions/automation/atmos.run#flag-translation). For `start`, the key `"transport"`
  becomes `--transport` and accepts `stdio`, `tcp`, or `websocket`, and the key `"address"` becomes
  `--address` for the `tcp` and `websocket` transports.
- **`args`**
  (Optional) A list or tuple of strings appended after the flags.
- **`working_directory`, `env`, `output`, `check`**

  (Optional) See [`atmos.run`](/functions/automation/atmos.run#arguments) for process options and defaults.

Options other than the positionals are keyword-only.

## Returns

A result with `stdout`, `stderr`, and `exit_code`. See [`atmos.run`](/functions/automation/atmos.run#returns) for output and error behavior.

## Examples

### Start a TCP server

```python
atmos.lsp("start", flags = {"transport": "tcp", "address": "localhost:7777"})
```

This runs `atmos lsp start --address=localhost:7777 --transport=tcp`. The call returns when the server exits.

### Start a WebSocket server on another port

```python
atmos.lsp("start", flags = {"transport": "websocket", "address": "localhost:9000"})
```

:::note
The language server runs until it is stopped, so the script waits at this call for the whole lifetime of the server.
With the default `stdio` transport the server speaks to an editor over standard input and output, which a script
rarely provides. Editors normally launch `atmos lsp start` themselves, and a script has little reason to call it
unless it supervises a `tcp` or `websocket` server.
:::

## Related

- [`atmos.run`](/functions/automation/atmos.run) runs any Atmos command from an argument list.
- [`atmos lsp start`](/cli/commands/lsp/start) documents the server and its transports.
- [Atmos Automation Language](/automation/language) and the [script step](/steps/type/script#calling-atmos-commands)