# Config editor

Edit `config.json` directly on the left or use the settings form on the right.
Both views update the same document. Open a local file or start with a new
configuration, then download the result for installation on your mirror host.

```{raw} html
<div id="mirror-config-editor">
  <p>Loading the configuration editor. JavaScript and an HTTP(S) connection are required.</p>
  <noscript>Enable JavaScript to use the editor. You can also use the configuration reference to edit your file manually.</noscript>
</div>
```

## Editing and validation

- Optional fields stay absent until you add them. Removing a field restores the
  runtime default; it is different from setting an empty string or `false`.
- Switching sync methods keeps existing options. Review any reported mismatch
  before downloading. Unknown fields and external plugin options remain in the
  JSON and can be edited there.
- Syntax errors, duplicate keys, and invalid settings block configuration
  downloads. During a syntax error, the form keeps its last valid view but is
  disabled. **Copy JSON** remains available to save an unfinished draft.
- Form edits participate in the JSON editor's undo history. Field changes preserve
  unrelated JSON text; **Format JSON** explicitly reformats the document.
- Validation checks the configuration structure and local option rules. It does
  not contact upstream repositories or check files, permissions, binaries, or
  signing keys on your server.

Files remain in this tab's memory. There is no upload, automatic storage, or
connection to the daemon. Download your changes before closing the page.
Per-plugin configuration files are separate and are not edited here.

The editor targets desktop browsers. When the window is narrow, use the JSON
and Settings tabs. For configuration details, see the
[configuration reference](configuration.md) and [sync methods](../sync-methods/index.md).