# The watch command

The `watch` command is useful when you want your book to be rendered on every
file change. You could repeatedly issue `mdbook build` every time a file is
changed. But using `mdbook watch` once will watch your files and will trigger
a build automatically whenever you modify a file.

#### Specify a directory

The `watch` command can take a directory as an argument to use as the book's
root instead of the current working directory.

```bash
mdbook watch path/to/book
```

#### --open

When you use the `--open` (`-o`) option, mdbook will open the rendered book in
your default web browser.

#### --dest-dir

The `--dest-dir` (`-d`) option allows you to change the output directory for
the book. If not specified it will default to the value of the
`build.build-dir` key in `book.toml`, or to `./book` relative to the book's
root directory.