# 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"
author = "John Doe"
description = "The example book covers examples."

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

[preprocessor.index]

[output.html]

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


## Supported configuration options

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

• 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.

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


### Build options

This controls the build process of your book.

• build-dir: The directory to put the rendered book in. By default this is book/ in the book’s root directory.

• 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.

## Configuring Preprocessors

The following preprocessors are available and included by default:

• links: Expand the {{ #playpen }} and {{ #include }} handlebars helpers in a chapter to include the contents of a file.
• index: Convert all chapter files named README.md into index.md. That is to say, all README.md would be rendered to an index file index.html in the rendered book.

book.toml

[build]
build-dir = "build"
create-missing = false

[preprocessor.index]


### Custom Preprocessor Configuration

Like renderers, preprocessor will need to be given its own table (e.g. [preprocessor.mathjax]). In the section, you may then pass extra configuration to the preprocessor by adding key-value pairs to the table.

For example

[preprocessor.links]
# set the renderers this preprocessor will run for
renderers = ["html"]
some_extra_feature = true


#### Locking a Preprocessor dependency to a renderer

You can explicitly specify that a preprocessor should run for a renderer by binding the two together.

[preprocessor.mathjax]
renderers = ["html"]  # mathjax only makes sense with the HTML renderer


By default when you add a [preprocessor.foo] table to your book.toml file, mdbook will try to invoke the mdbook-foo executable. If you want to use a different program name or pass in command-line arguments, this behaviour can be overridden by adding a command field.

[preprocessor.random]
command = "python random.py"


## Configuring Renderers

### HTML renderer options

The HTML renderer has a couple of options as well. All the options for the renderer need to be specified under the TOML table [output.html].

The following configuration options are available:

• theme: mdBook comes with a default theme and all the resource files needed for it. But if this option is set, mdBook will selectively overwrite the theme files with the ones found in the specified folder.
• default-theme: The theme color scheme to select by default in the ‘Change Theme’ dropdown. Defaults to light.
• curly-quotes: Convert straight quotes to curly quotes, except for those that occur in code blocks and code spans. Defaults to false.
• mathjax-support: Adds support for MathJax. Defaults to false.
• google-analytics: If you use Google Analytics, this option lets you enable it by simply specifying your ID in the configuration file.
• additional-css: If you need to slightly change the appearance of your book without overwriting the whole style, you can specify a set of stylesheets that will be loaded after the default ones where you can surgically change the style.
• additional-js: If you need to add some behaviour to your book without removing the current behaviour, you can specify a set of JavaScript files that will be loaded alongside the default one.
• no-section-label: mdBook by defaults adds section label in table of contents column. For example, “1.”, “2.1”. Set this option to true to disable those labels. Defaults to false.
• playpen: A subtable for configuring various playpen settings.
• search: A subtable for configuring the in-browser search functionality. mdBook must be compiled with the search feature enabled (on by default).
• git-repository-url: A url to the git repository for the book. If provided an icon link will be output in the menu bar of the book.
• git-repository-icon: The FontAwesome icon class to use for the git repository link. Defaults to fa-github.

Available configuration options for the [output.html.playpen] table:

• editable: Allow editing the source code. Defaults to false.
• copy-js: Copy JavaScript files for the editor to the output directory. Defaults to true.

Available configuration options for the [output.html.search] table:

• enable: Enables the search feature. Defaults to true.
• limit-results: The maximum number of search results. Defaults to 30.
• teaser-word-count: The number of words used for a search result teaser. Defaults to 30.
• use-boolean-and: Define the logical link between multiple search words. If true, all search words must appear in each result. Defaults to true.
• boost-title: Boost factor for the search result score if a search word appears in the header. Defaults to 2.
• boost-hierarchy: Boost factor for the search result score if a search word appears in the hierarchy. The hierarchy contains all titles of the parent documents and all parent headings. Defaults to 1.
• boost-paragraph: Boost factor for the search result score if a search word appears in the text. Defaults to 1.
• expand: True if search should match longer results e.g. search micro should match microwave. Defaults to true.
• heading-split-level: Search results will link to a section of the document which contains the result. Documents are split into sections by headings this level or less. Defaults to 3. (### This is a level 3 heading)
• copy-js: Copy JavaScript files for the search implementation to the output directory. Defaults to true.

This shows all available HTML output options in the book.toml:

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

[output.html]
theme = "my-theme"
default-theme = "light"
curly-quotes = true
mathjax-support = false
no-section-label = false
git-repository-url = "https://github.com/rust-lang-nursery/mdBook"
git-repository-icon = "fa-github"

[output.html.playpen]
editable = false
copy-js = true

[output.html.search]
enable = true
limit-results = 30
teaser-word-count = 30
use-boolean-and = true
boost-title = 2
boost-hierarchy = 1
boost-paragraph = 1
expand = true
copy-js = true


### Custom Renderers

A custom renderer can be enabled by adding a [output.foo] table to your book.toml. Similar to preprocessors this will instruct mdbook to pass a representation of the book to mdbook-foo for rendering.

Custom renderers will have access to all configuration within their table (i.e. anything under [output.foo]), and the command to be invoked can be manually specified with the command field.

## Environment Variables

All configuration values can be overridden from the command line by setting the corresponding environment variable. Because many operating systems restrict environment variables to be alphanumeric characters or _, the configuration key needs to be formatted slightly differently to the normal foo.bar.baz form.

Variables starting with MDBOOK_ are used for configuration. The key is created by removing the MDBOOK_ prefix and turning the resulting string into kebab-case. Double underscores (__) separate nested keys, while a single underscore (_) is replaced with a dash (-).

For example:

• MDBOOK_foo -> foo
• MDBOOK_FOO -> foo
• MDBOOK_FOO__BAR -> foo.bar
• MDBOOK_FOO_BAR -> foo-bar
• MDBOOK_FOO_bar__baz -> foo-bar.baz

So by setting the MDBOOK_BOOK__TITLE environment variable you can override the book’s title without needing to touch your book.toml.

Note: To facilitate setting more complex config items, the value of an environment variable is first parsed as JSON, falling back to a string if the parse fails.

This means, if you so desired, you could override all book metadata when building the book with something like

$export MDBOOK_BOOK="{'title': 'My Awesome Book', authors: ['Michael-F-Bryan']}"$ mdbook build


The latter case may be useful in situations where mdbook is invoked from a script or CI, where it sometimes isn’t possible to update the book.toml before building.