# General Configuration

You can configure the parameters for your book in the book.toml file.

Here is an example of what a book.toml file might look like:

    [book]
    title = "Example book"
    authors = ["John Doe"]
    description = "The example book covers examples."

    [rust]
    edition = "2018"

    [build]
    build-dir = "my-example-book"
    create-missing = false

    [preprocessor.index]

    [preprocessor.links]

    [output.html]
    additional-css = ["custom.css"]

    [output.html.search]
    limit-results = 15

## Supported configuration options

It is important to note that any relative path specified in the configuration will always be taken relative from the root of the book where the configuration file is located.

### General metadata

This is general information about your book.

- title: The title of the book
- authors: The author(s) of the book
- description: A description for the book, which is added as meta information in the html `<head>` of each page
- src: By default, the source directory is found in the directory named `src` directly under the root folder. But this is configurable with the `src` key in the configuration file.
- language: The main language of the book, which is used as a language attribute `<html lang="en">` for example. This is also used to derive the direction of text (RTL, LTR) within the book.
- text-direction: The direction of text in the book: Left-to-right (LTR) or Right-to-left (RTL). Possible values: `ltr`, `rtl`. When not specified, the text direction is derived from the book’s `language` attribute.

book.toml

    [book]
    title = "Example book"
    authors = ["John Doe", "Jane Doe"]
    description = "The example book covers examples."
    src = "my-src"  # the source files will be found in `root/my-src` instead of `root/src`
    language = "en"
    text-direction = "ltr"

### Rust options

Options for the Rust language, relevant to running tests and playground integration.

    [rust]
    edition = "2015"   # the default edition for code blocks

- edition: Rust edition to use by default for the code snippets. Default is `"2015"`. Individual code blocks can be controlled with the `edition2015`, `edition2018` or `edition2021` annotations, such as:

      ```rust,edition2015
      // This only works in 2015.
      let try = true;
      ```

### Build options

This controls the build process of your book.

    [build]
    build-dir = "book"                # the directory where the output is placed
    create-missing = true             # whether or not to create missing pages
    use-default-preprocessors = true  # use the default preprocessors
    extra-watch-dirs = []             # directories to watch for triggering builds

- build-dir: The directory to put the rendered book in. By default this is `book/` in the book’s root directory. This can overridden with the `--dest-dir` CLI option.

- create-missing: By default, any missing files specified in `SUMMARY.md` will be created when the book is built (i.e. `create-missing = true`). If this is `false` then the build process will instead exit with an error if any files do not exist.

- use-default-preprocessors: Disable the default preprocessors (of `links` & `index`) by setting this option to `false`.

  If you have the same, and/or other preprocessors declared via their table of configuration, they will run instead.

  - For clarity, with no preprocessor configuration, the default `links` and `index` will run.
  - Setting `use-default-preprocessors = false` will disable these default preprocessors from running.
  - Adding `[preprocessor.links]`, for example, will ensure, regardless of `use-default-preprocessors` that `links` it will run.

- extra-watch-dirs: A list of paths to directories that will be watched in the `watch` and `serve` commands. Changes to files under these directories will trigger rebuilds. Useful if your book depends on files outside its `src` directory.