Configuration

Guide to all available configuration settings.

Introduction

Project settings are configured by default using a YAML configuration file in the project directory named mkdocs.yml. You can specify another path for it by using the -f/--config-file option (see mkdocs build --help).

As a minimum, this configuration file must contain the site_name. All other settings are optional.

Project information

site_name

This is a required setting, and should be a string that is used as the main title for the project documentation. For example:

site_name: Marshmallow Generator

When rendering the theme this setting will be passed as the site_name context variable.

site_url

Set the canonical URL of the site. This will add a link tag with the canonical URL to the head section of each HTML page. If the 'root' of the MkDocs site will be within a subdirectory of a domain, be sure to include that subdirectory in the setting (https://example.com/foo/).

This setting is also used for mkdocs serve: the server will be mounted onto a path taken from the path component of the URL, e.g. some/page.md will be served from http://127.0.0.1:8000/foo/some/page/ to mimic the expected remote layout.

default: null

repo_url

When set, provides a link to your repository (GitHub, Bitbucket, GitLab, ...) on each page.

repo_url: https://github.com/example/repository/

default: null

repo_name

When set, provides the name for the link to your repository on each page.

default: 'GitHub', 'Bitbucket' or 'GitLab' if the repo_url matches those domains, otherwise the hostname from the repo_url.

edit_uri

The path from the base repo_url to the docs directory when directly viewing a page, accounting for specifics of the repository host (e.g. GitHub, Bitbucket, etc), the branch, and the docs directory itself. MkDocs concatenates repo_url and edit_uri, and appends the input path of the page.

When set, and if your theme supports it, provides a link directly to the page in your source repository. This makes it easier to find and edit the source for the page. If repo_url is not set, this option is ignored. On some themes, setting this option may cause an edit link to be used in place of a repository link. Other themes may show both links.

The edit_uri supports query ('?') and fragment ('#') characters. For repository hosts that use a query or a fragment to access the files, the edit_uri might be set as follows. (Note the ? and # in the URI...)

# Query string example
edit_uri: '?query=root/path/docs/'

# Hash fragment example
edit_uri: '#root/path/docs/'

For other repository hosts, simply specify the relative path to the docs directory.

# Query string example
edit_uri: root/path/docs/

For example, having this config:

repo_url: https://example.com/project/repo
edit_uri: blob/main/docs/

means that a page named 'foo/bar.md' will have its edit link lead to:
https://example.com/project/repo/blob/main/docs/foo/bar.md

edit_uri can actually be just an absolute URL, not necessarily relative to repo_url, so this can achieve the same result:

edit_uri: https://example.com/project/repo/blob/main/docs/

For more flexibility, see edit_uri_template below.

default: edit/master/docs/ for GitHub and GitLab repos or src/default/docs/ for a Bitbucket repo, if repo_url matches those domains, otherwise null

edit_uri_template

The more flexible variant of edit_uri. These two are equivalent:

edit_uri: 'blob/main/docs/'
edit_uri_template: 'blob/main/docs/{path}'

(they are also mutually exclusive -- don't specify both).

Starting from here, you can change the positioning or formatting of the path, in case the default behavior of appending the path isn't enough.

The contents of edit_uri_template are normal Python format strings, with only these fields available:

• {path}, e.g. foo/bar.md
• {path_noext}, e.g. foo/bar

And the conversion flag !q is available, to percent-encode the field:

• {path!q}, e.g. foo%2Fbar.md

? NOTE: Suggested useful configurations:

• GitHub Wiki:
  (e.g. https://github.com/project/repo/wiki/foo/bar/_edit)

  repo_url: 'https://github.com/project/repo/wiki'
  edit_uri_template: '{path_noext}/_edit'

• BitBucket editor:
  (e.g. https://bitbucket.org/project/repo/src/master/docs/foo/bar.md?mode=edit)

  repo_url: 'https://bitbucket.org/project/repo/'
  edit_uri_template: 'src/master/docs/{path}?mode=edit'

• GitLab Static Site Editor:
  (e.g. https://gitlab.com/project/repo/-/sse/master/docs%2Ffoo%2bar.md)

  repo_url: 'https://gitlab.com/project/repo'
  edit_uri_template: '-/sse/master/docs%2F{path!q}'

• GitLab Web IDE:
  (e.g. https://gitlab.com/-/ide/project/repo/edit/master/-/docs/foo/bar.md)

  edit_uri_template: 'https://gitlab.com/-/ide/project/repo/edit/master/-/docs/{path}'

default: null

site_description

Set the site description. This will add a meta tag to the generated HTML header.

default: null

site_author

Set the name of the author. This will add a meta tag to the generated HTML header.

default: null

copyright

Set the copyright information to be included in the documentation by the theme.

default: null

remote_branch

Set the remote branch to commit to when using gh-deploy to deploy to GitHub Pages. This option can be overridden by a command line option in gh-deploy.

default: gh-pages

remote_name

Set the remote name to push to when using gh-deploy to deploy to GitHub Pages. This option can be overridden by a command line option in gh-deploy.

default: origin

Documentation layout

nav

This setting is used to determine the format and layout of the global navigation for the site. A minimal navigation configuration could look like this:

nav:
  - 'index.md'
  - 'about.md'

All paths in the navigation configuration must be relative to the docs_dir configuration option. See the section on configuring pages and navigation for a more detailed breakdown, including how to create sub-sections.

Navigation items may also include links to external sites. While titles are optional for internal links, they are required for external links. An external link may be a full URL or a relative URL. Any path which is not found in the files is assumed to be an external link. See the section about Meta-Data on how MkDocs determines the page title of a document.

nav:
  - Introduction: 'index.md'
  - 'about.md'
  - 'Issue Tracker': 'https://example.com/'

In the above example, the first two items point to local files while the third points to an external site.

However, sometimes the MkDocs site is hosted in a subdirectory of a project's site and you may want to link to other parts of the same site without including the full domain. In that case, you may use an appropriate relative URL.

site_url: https://example.com/foo/

nav:
  - Home: '../'
  - 'User Guide': 'user-guide.md'
  - 'Bug Tracker': '/bugs/'

In the above example, two different styles of external links are used. First, note that the site_url indicates that the MkDocs site is hosted in the /foo/ subdirectory of the domain. Therefore, the Home navigation item is a relative link that steps up one level to the server root and effectively points to https://example.com/. The Bug Tracker item uses an absolute path from the server root and effectively points to https://example.com/bugs/. Of course, the User Guide points to a local MkDocs page.

default: By default nav will contain an alphanumerically sorted, nested list of all the Markdown files found within the docs_dir and its sub-directories. Index files will always be listed first within a sub-section.

exclude_docs

This config defines patterns of files (under docs_dir) to not be picked up into the built site.

Example:

exclude_docs: |
  api-config.json    # A file with this name anywhere.
  /requirements.txt  # Top-level "docs/requirements.txt".
  *.py               # Any file with this extension anywhere.
  !/foo/example.py   # But keep this particular file.

This follows the .gitignore pattern format.

The following defaults are always implicitly prepended - to exclude dot-files (and directories) as well as the top-level templates directory:

exclude_docs: |
  .*
  /templates/

So, in order to really start this config fresh, you'd need to specify a negated version of these entries first.

Otherwise you could for example opt only certain dot-files back into the site:

exclude_docs: |
  !.assets  # Don't exclude '.assets' although all other '.*' are excluded

draft_docs

This config defines patterns of files (under docs_dir) to be treated as a draft. Draft files are available during mkdocs serve and include a "DRAFT" mark but will not be included in the build. To prevent this effect and make "serve" behave the same as "build", you can run mkdocs serve --clean.

Example:

draft_docs: |
  drafts/               # A "drafts" directory anywhere.
  _unpublished.md       # A md file ending in _unpublished.md
  !/foo_unpublished.md  # But keep this particular file.

This follows the .gitignore pattern format.

not_in_nav

If you want to include some docs into the site but intentionally exclude them from the nav, normally MkDocs warns about this.

Adding such patterns of files (relative to docs_dir) into the not_in_nav config will prevent such warnings.

Example:

nav:
  - Foo: foo.md
  - Bar: bar.md

not_in_nav: |
  /private.md

As the previous option, this follows the .gitignore pattern format.

validation

Configure the strictness of MkDocs' diagnostic messages when validating links to documents.

This is a tree of configs, and for each one the value can be one of the three: warn, info, ignore. Which cause a logging message of the corresponding severity to be produced. The warn level is, of course, intended for use with mkdocs build --strict (where it becomes an error), which you can employ in continuous testing.

The config validation.links.absolute_links additionally has a special value relative_to_docs, for validation of absolute links.

? EXAMPLE: Defaults of this config as of MkDocs 1.6:

validation:
  nav:
    omitted_files: info
    not_found: warn
    absolute_links: info
  links:
    not_found: warn
    anchors: info
    absolute_links: info
    unrecognized_links: info

(Note: you shouldn't copy this whole example, because it only duplicates the defaults. Only individual items that differ should be set.)

The defaults of some of the behaviors already differ from MkDocs 1.4 and below - they were ignored before.

? EXAMPLE: Configure MkDocs 1.6 to behave like MkDocs 1.4 and below (reduce strictness):

validation:
  absolute_links: ignore
  unrecognized_links: ignore
  anchors: ignore

! EXAMPLE: Recommended settings for most sites (maximal strictness):

validation:
  omitted_files: warn
  absolute_links: warn  # Or 'relative_to_docs' - new in MkDocs 1.6
  unrecognized_links: warn
  anchors: warn  # New in MkDocs 1.6

Note how in the above examples we omitted the 'nav' and 'links' keys. Here absolute_links: means setting both nav: absolute_links: and links: absolute_links:.

Full list of values and examples of log messages that they can hide or make more prominent:

• validation.nav.omitted_files

  • The following pages exist in the docs directory, but are not included in the "nav" configuration: ...

• validation.nav.not_found

  • A reference to 'foo/bar.md' is included in the 'nav' configuration, which is not found in the documentation files.

  • A reference to 'foo/bar.md' is included in the 'nav' configuration, but this file is excluded from the built site.

• validation.nav.absolute_links

  • An absolute path to '/foo/bar.html' is included in the 'nav' configuration, which presumably points to an external resource.

• validation.links.not_found

  • Doc file 'example.md' contains a link '../foo/bar.md', but the target is not found among documentation files.

  • Doc file 'example.md' contains a link to 'foo/bar.md' which is excluded from the built site.

• validation.links.anchors

  • Doc file 'example.md' contains a link '../foo/bar.md#some-heading', but the doc 'foo/bar.md' does not contain an anchor '#some-heading'.

  • Doc file 'example.md' contains a link '#some-heading', but there is no such anchor on this page.

• validation.links.absolute_links

  • Doc file 'example.md' contains an absolute link '/foo/bar.html', it was left as is. Did you mean 'foo/bar.md'?

• validation.links.unrecognized_links

  • Doc file 'example.md' contains an unrecognized relative link '../foo/bar/', it was left as is. Did you mean 'foo/bar.md'?

  • Doc file 'example.md' contains an unrecognized relative link 'mail@example.com', it was left as is. Did you mean 'mailto:mail@example.com'?

Validation of absolute links

Historically, within Markdown, MkDocs only recognized relative links that lead to another physical *.md document (or media file). This is a good convention to follow because then the source pages are also freely browsable without MkDocs, for example on GitHub. Whereas absolute links were left unmodified (making them often not work as expected) or, more recently, warned against. If you dislike having to always use relative links, now you can opt into absolute links and have them work correctly.

If you set the setting validation.links.absolute_links to the new value relative_to_docs, all Markdown links starting with / will be understood as being relative to the docs_dir root. The links will then be validated for correctness according to all the other rules that were already working for relative links in prior versions of MkDocs. For the HTML output, these links will still be turned relative so that the site still works reliably.

So, now any document (e.g. "dir1/foo.md") can link to the document "dir2/bar.md" as [link](/dir2/bar.md), in addition to the previously only correct way [link](../dir2/bar.md).

You have to enable the setting, though. The default is still to just skip the link.

validation:
  links:
    absolute_links: relative_to_docs
    anchors: warn
    unrecognized_links: warn

Build directories

theme

Sets the theme and theme specific configuration of your documentation site. May be either a string or a set of key/value pairs.

If a string, it must be the string name of a known installed theme. For a list of available themes visit Choosing Your Theme.

An example set of key/value pairs might look something like this:

theme:
  name: mkdocs
  locale: en
  custom_dir: my_theme_customizations/
  static_templates:
    - sitemap.html
  include_sidebar: false

If a set of key/value pairs, the following nested keys can be defined:

default: 'mkdocs'

docs_dir

The directory containing the documentation source markdown files. This can either be a relative directory, in which case it is resolved relative to the directory containing your configuration file, or it can be an absolute directory path from the root of your local file system.

default: 'docs'

site_dir

The directory where the output HTML and other files are created. This can either be a relative directory, in which case it is resolved relative to the directory containing your configuration file, or it can be an absolute directory path from the root of your local file system.

default: 'site'

site/

extra_css

Set a list of CSS files (relative to docs_dir) to be included by the theme, typically as <link> tags.

Example:

extra_css:
  - css/extra.css
  - css/second_extra.css

default: [] (an empty list).

extra_javascript

Set a list of JavaScript files in your docs_dir to be included by the theme, as <script> tags.

See the examples and what they produce:

extra_javascript:
  - some_plain_javascript.js       # <script src="some_plain_javascript.js"></script>
        # New behavior in MkDocs 1.5:
  - implicitly_as_module.mjs       # <script src="implicitly_as_module.mjs" type="module"></script>
        # Config keys only supported since MkDocs 1.5:
  - path: explicitly_as_module.mjs # <script src="explicitly_as_module.mjs" type="module"></script>
    type: module
  - path: deferred_plain.js        # <script src="deferred_plain.js" defer></script>
    defer: true
  - path: scripts/async_module.mjs # <script src="scripts/async_module.mjs" type="module" async></script>
    type: module
    async: true

So, each item can be either:

• a plain string, or
• a mapping that has the required path key and 3 optional keys type (string), async (boolean), defer (boolean).

Only the plain string variant detects the .mjs extension and adds type="module", otherwise type: module must be written out regardless of extension.

default: [] (an empty list).

extra_templates

Set a list of templates in your docs_dir to be built by MkDocs. To see more about writing templates for MkDocs read the documentation about custom themes and specifically the section about the available variables to templates. See the example in extra_css for usage.

default: [] (an empty list).

extra

A set of key-value pairs, where the values can be any valid YAML construct, that will be passed to the template. This allows for great flexibility when creating custom themes.

For example, if you are using a theme that supports displaying the project version, you can pass it to the theme like this:

extra:
  version: 1.0

default: By default extra will be an empty key-value mapping.

Preview controls

Live Reloading

watch

Determines additional directories to watch when running mkdocs serve. Configuration is a YAML list.

watch:
  - directory_a
  - directory_b

Allows a custom default to be set without the need to pass it through the -w/--watch option every time the mkdocs serve command is called.

use_directory_urls

This setting controls the style used for linking to pages within the documentation.

The following table demonstrates how the URLs used on the site differ when setting use_directory_urls to true or false.

The default style of use_directory_urls: true creates more user friendly URLs, and is usually what you'll want to use.

The alternate style can be useful if you want your documentation to remain properly linked when opening pages directly from the file system, because it creates links that point directly to the target file rather than the target directory.

default: true

strict

Determines how warnings are handled. Set to true to halt processing when a warning is raised. Set to false to print a warning and continue processing.

This is also available as a command line flag: --strict.

default: false

dev_addr

Determines the address used when running mkdocs serve. Must be of the format IP:PORT.

Allows a custom default to be set without the need to pass it through the --dev-addr option every time the mkdocs serve command is called.

default: '127.0.0.1:8000'

See also: site_url.

Formatting options

markdown_extensions

MkDocs uses the Python Markdown library to translate Markdown files into HTML. Python Markdown supports a variety of extensions that customize how pages are formatted. This setting lets you enable a list of extensions beyond the ones that MkDocs uses by default (meta, toc, tables, and fenced_code).

For example, to enable the SmartyPants typography extension, use:

markdown_extensions:
  - smarty

Some extensions provide configuration options of their own. If you would like to set any configuration options, then you can nest a key/value mapping (option_name: option value) of any options that a given extension supports. See the documentation for the extension you are using to determine what options they support.

For example, to enable permalinks in the (included) toc extension, use:

markdown_extensions:
  - toc:
      permalink: true

Note that a colon (:) must follow the extension name (toc) and then on a new line the option name and value must be indented and separated by a colon. If you would like to define multiple options for a single extension, each option must be defined on a separate line:

markdown_extensions:
  - toc:
      permalink: true
      separator: "_"

Add an additional item to the list for each extension. If you have no configuration options to set for a specific extension, then simply omit options for that extension:

markdown_extensions:
  - smarty
  - toc:
      permalink: true
  - sane_lists

In the above examples, each extension is a list item (starts with a -). As an alternative, key/value pairs can be used instead. However, in that case an empty value must be provided for extensions for which no options are defined. Therefore, the last example above could also be defined as follows:

markdown_extensions:
  smarty: {}
  toc:
    permalink: true
  sane_lists: {}

This alternative syntax is required if you intend to override some options via inheritance.

default: [] (an empty list).

hooks

A list of paths to Python scripts (relative to mkdocs.yml) that are loaded and used as plugin instances.

For example:

hooks:
  - my_hooks.py

Then the file my_hooks.py can contain any plugin event handlers (without self), e.g.:

def on_page_markdown(markdown, **kwargs):
    return markdown.replace('a', 'z')

? EXAMPLE: Advanced example:

This produces warnings based on the Markdown content (and warnings are fatal in strict mode):

import logging, re
import mkdocs.plugins

log = logging.getLogger('mkdocs')

@mkdocs.plugins.event_priority(-50)
def on_page_markdown(markdown, page, **kwargs):
    path = page.file.src_uri
    for m in re.finditer(r'\bhttp://[^) ]+', markdown):
        log.warning(f"Documentation file '{path}' contains a non-HTTPS link: {m[0]}")

This does not enable any new abilities compared to plugins, it only simplifies one-off usages, as these don't need to be installed like plugins do.

Note that for mkdocs serve the hook module will not be reloaded on each build.

You might have seen this feature in the mkdocs-simple-hooks plugin. If using standard method names, it can be directly replaced, e.g.:

-plugins:
-  - mkdocs-simple-hooks:
-      hooks:
-        on_page_markdown: 'my_hooks:on_page_markdown'
+hooks:
+  - my_hooks.py

plugins

A list of plugins (with optional configuration settings) to use when building the site. See the Plugins documentation for full details.

default: ['search'] (the "search" plugin included with MkDocs).

If the plugins config setting is defined in the mkdocs.yml config file, then any defaults (such as search) are ignored and you need to explicitly re-enable the defaults if you would like to continue using them:

plugins:
  - search
  - your_other_plugin

To define options for a given plugin, use a nested set of key/value pairs:

plugins:
  - search
  - your_other_plugin:
      option1: value
      option2: other value

To completely disable all plugins, including any defaults, set the plugins setting to an empty list:

plugins: []

enabled option

plugins:
  - search
  - code-validator:
      enabled: !ENV [LINT, false]

Alternate syntax

In the above examples, each plugin is a list item (starts with a -). As an alternative, key/value pairs can be used instead. However, in that case an empty value must be provided for plugins for which no options are defined. Therefore, the last example above could also be defined as follows:

plugins:
  search: {}
  your_other_plugin:
    option1: value
    option2: other value

This alternative syntax is required if you intend to override some options via inheritance.

Search

A search plugin is provided by default with MkDocs which uses lunr.js as a search engine. The following config options are available to alter the behavior of the search plugin:

separator

A regular expression which matches the characters used as word separators when building the index. By default whitespace and the hyphen (-) are used. To add the dot (.) as a word separator you might do this:

plugins:
  - search:
      separator: '[\s\-\.]+'

default: '[\s\-]+'

min_search_length

An integer value that defines the minimum length for a search query. By default searches shorter than 3 chars in length are ignored as search result quality with short search terms are poor. However, for some use cases (such as documentation about Message Queues which might generate searches for 'MQ') it may be preferable to set a shorter limit.

plugins:
  - search:
      min_search_length: 2

default: 3

lang

A list of languages to use when building the search index as identified by their ISO 639-1 language codes. With Lunr Languages, the following languages are supported:

• ar: Arabic
• da: Danish
• nl: Dutch
• en: English
• fi: Finnish
• fr: French
• de: German
• hu: Hungarian
• it: Italian
• ja: Japanese
• no: Norwegian
• pt: Portuguese
• ro: Romanian
• ru: Russian
• es: Spanish
• sv: Swedish
• th: Thai
• tr: Turkish
• vi: Vietnamese

You may contribute additional languages.

default: The value of theme.locale if set, otherwise [en].

prebuild_index

Optionally generates a pre-built index of all pages, which provides some performance improvements for larger sites. Before enabling, confirm that the theme you are using explicitly supports using a prebuilt index (the builtin themes do). Set to true to enable.

default: False

indexing

Configures what strategy the search indexer will use when building the index for your pages. This property is particularly useful if your project is large in scale, and the index takes up an enormous amount of disk space.

plugins:
  - search:
      indexing: 'full'

Options

default: full

Special YAML tags

Environment variables

In most cases, the value of a configuration option is set directly in the configuration file. However, as an option, the value of a configuration option may be set to the value of an environment variable using the !ENV tag. For example, to set the value of the site_name option to the value of the variable SITE_NAME the YAML file may contain the following:

site_name: !ENV SITE_NAME

If the environment variable is not defined, then the configuration setting would be assigned a null (or None in Python) value. A default value can be defined as the last value in a list. Like this:

site_name: !ENV [SITE_NAME, 'My default site name']

Multiple fallback variables can be used as well. Note that the last value is not an environment variable, but must be a value to use as a default if none of the specified environment variables are defined.

site_name: !ENV [SITE_NAME, OTHER_NAME, 'My default site name']

Simple types defined within an environment variable such as string, bool, integer, float, datestamp and null are parsed as if they were defined directly in the YAML file, which means that the value will be converted to the appropriate type. However, complex types such as lists and key/value pairs cannot be defined within a single environment variable.

For more details, see the pyyaml_env_tag project.

Paths relative to the current file or site

Some Markdown extensions can benefit from knowing the path of the Markdown file that's currently being processed, or just the root path of the current site. For that, the special tag !relative can be used in most contexts within the config file, though the only known usecases are within markdown_extensions.

Examples of the possible values are:

- !relative  # Relative to the directory of the current Markdown file
- !relative $docs_dir  # Path of the docs_dir
- !relative $config_dir  # Path of the directory that contains the main mkdocs.yml
- !relative $config_dir/some/child/dir  # Some subdirectory of the root config directory

(Here, $docs_dir and $config_dir are currently the only special prefixes that are recognized.)

Example:

markdown_extensions:
  - pymdownx.snippets:
      base_path: !relative  # Relative to the current Markdown file

This allows the pymdownx.snippets extension to include files relative to the current Markdown file, which without this tag it would have no way of knowing.

markdown_extensions:
  - pymdownx.snippets:
      base_path: !relative $config_dir  # Relative to the root directory with mkdocs.yml

Configuration Inheritance

Generally, a single file would hold the entire configuration for a site. However, some organizations may maintain multiple sites which all share a common configuration across them. Rather than maintaining separate configurations for each, the common configuration options can be defined in a parent configuration file which each site's primary configuration file inherits.

To define the parent for a configuration file, set the INHERIT (all caps) key to the path of the parent file. The path must be relative to the location of the primary file.

For configuration options to be merged with a parent configuration, those options must be defined as key/value pairs. Specifically, the markdown_extensions and plugins options must use the alternative syntax which does not use list items (lines which start with -).

For example, suppose the common (parent) configuration is defined in base.yml:

theme:
  name: mkdocs
  locale: en
  highlightjs: true

markdown_extensions:
  toc:
    permalink: true
  admonition: {}

Then, for the "foo" site, the primary configuration file would be defined at foo/mkdocs.yml:

INHERIT: ../base.yml
site_name: Foo Project
site_url: https://example.com/foo

When running mkdocs build, the file at foo/mkdocs.yml would be passed in as the configuration file. MkDocs will then parse that file, retrieve and parse the parent file base.yml and deep merge the two. This would result in MkDocs receiving the following merged configuration:

site_name: Foo Project
site_url: https://example.com/foo

theme:
  name: mkdocs
  locale: en
  highlightjs: true

markdown_extensions:
  toc:
    permalink: true
  admonition: {}

Deep merging allows you to add and/or override various values in your primary configuration file. For example, suppose for one site you wanted to add support for definition lists, use a different symbol for permalinks, and define a different separator. In that site's primary configuration file you could do:

INHERIT: ../base.yml
site_name: Bar Project
site_url: https://example.com/bar

markdown_extensions:
  def_list: {}
  toc:
    permalink: 
    separator: "_"

In that case, the above configuration would be deep merged with base.yml and result in the following configuration:

site_name: Bar Project
site_url: https://example.com/bar

theme:
  name: mkdocs
  locale: en
  highlightjs: true

markdown_extensions:
  def_list: {}
  toc:
    permalink: 
    separator: "_"
  admonition: {}

Notice that the admonition extension was retained from the parent configuration, the def_list extension was added, the value of toc.permalink was replaced, and the value of toc.separator was added.

You can replace or merge the value of any key. However, any non-key is always replaced. Therefore, you cannot append items to a list. You must redefine the entire list.

As the nav configuration is made up of nested lists, this means that you cannot merge navigation items. Of course, you can replace the entire nav configuration with a new one. However, it is generally expected that the entire navigation would be defined in the primary configuration file for a project.

The inheritance can also be used as a quick way to override keys on the command line - by using stdin as the config file. For example:

echo '{INHERIT: mkdocs.yml, site_name: "Renamed site"}' | mkdocs build -f -