ExDoc

ExDoc is a tool to generate documentation for Erlang and Elixir projects. To see an example, you can access Elixir's official docs.

Features

ExDoc ships with many features:

Automatically generates online- and offline-accessible HTML and EPUB documents from your API documentation.
Responsive design, covering phones and tablets.
Support for custom pages, guides, livebooks and cheatsheets.
Support for custom grouping of modules, functions, and pages in the sidebar.
Customizable logo.
A direct link back to the source code for every documented entity.
Full-text search.
Keyboard shortcuts. (Press ? to show help.)
Quick-search with autocompletion support. (s keyboard shortcut.)
Go-to shortcut with auto-complete to take the reader to any HexDocs package documentation. (g keyboard shortcut.)
Support for night mode, activated according to the browser preference.
Tooltips for links to modules and functions, both for the current project and other projects.
Version dropdown, automatically configured when hosted on HexDocs.

Usage

You can use ExDoc with Mix (recommended for Elixir projects), with Rebar (recommended for Erlang projects), or via the command line.

Mix

ExDoc requires Elixir v1.12 or later. Then add ExDoc as a dependency:

def deps do
  [
    {:ex_doc, "~> 0.34", only: :dev, runtime: false},
  ]
end

Then run mix deps.get.

Erlang development environment {: .warning}

Some Operating System distributions split Erlang into multiple packages, and at least one ExDoc dependency (earmark_parser) requires the Erlang development environment. If you see a message like "/usr/lib/erlang/lib/parsetools-2.3.1/include/yeccpre.hrl: no such file or directory", it means you lack this environment. For instance, on the Debian operating system and its derivatives, you need to apt install erlang-dev.

ExDoc will automatically pull in information from your projects, such as the application and version. However, you may want to set :name, :source_url and :homepage_url in order to have nicer output from ExDoc:

def project do
  [
    app: :my_app,
    version: "0.1.0-dev",
    deps: deps(),

    # Docs
    name: "MyApp",
    source_url: "https://github.com/USER/PROJECT",
    homepage_url: "http://YOUR_PROJECT_HOMEPAGE",
    docs: [
      main: "MyApp", # The main page in the docs
      logo: "path/to/logo.png",
      extras: ["README.md"]
    ]
  ]
end

Now you are ready to generate your project documentation with mix docs. To see all options available, run mix help docs.

To learn about how to document your projects, see Elixir's writing documentation page.

Rebar3

From Erlang/OTP 24+, you can use ExDoc to render your Erlang documentation written with EDoc. See rebar3_ex_doc for more information.

CLI

You can use ExDoc via the command line.

Install ExDoc as an escript:
```
$ mix escript.install hex ex_doc
```
Now you are ready to use it in your projects. Move into your project directory and make sure it's compiled:
```
$ cd PATH_TO_YOUR_PROJECT
$ mix compile
```

Invoke the ex_doc executable from your project:

$ ex_doc "PROJECT_NAME" "PROJECT_VERSION" _build/dev/lib/project/ebin -m "PROJECT_MODULE" -u "https://github.com/GITHUB_USER/GITHUB_REPO" -l path/to/logo.png

Examples of appropriate values:

PROJECT_NAME    => Ecto
PROJECT_VERSION => 0.1.0
PROJECT_MODULE  => Ecto (the main module provided by the library)
GITHUB_USER     => elixir-lang
GITHUB_REPO     => ecto

You can specify a config file via the --config option, both Elixir and Erlang formats are supported. Invoke ex_doc without arguments to learn more.

Syntax highlighting

ExDoc uses the makeup project for syntax highlighting. By default, highlighters for Erlang and Elixir are included. To syntax-highlight other languages, simply add the equivalent makeup_LANGUAGE package to your mix.exs/rebar.config file. For example, for HTML support you would add:

Elixir (Mix)

{:makeup_html, ">= 0.0.0", only: :dev, runtime: false}

Erlang (Rebar3)

{makeup_html, "0.1.1"}

You can find all supported languages under the Makeup organization on GitHub and view them at Makeup's website.

Additional pages

You can publish additional pages in your project documentation by configuring them as :extras. The following formats and extensions are supported:

Markdown (.md extension) - useful for general long-term text. Learn more.
Cheatsheets (.cheatmd extension) - useful for discovery and quick reference. Learn more.
Livebooks (.livemd extension) - useful for tutorials, interactive examples, and deep dives. Learn more.

For example, you can set your :extras to:

Elixir

extras: ["README.md", "LICENSE", "tutorial.livemd", "cheatsheet.cheatmd"]

Run mix help docs for more information on configuration.

Erlang

{extras, [<<"README.md">>, <<"cheatsheet.cheatmd">>]}.

Metadata

ExDoc supports metadata keys in your documentation.

Elixir

In Elixir, you can add metadata to modules and functions.

For a module, use @moduledoc, which is equivalent to adding the annotation to everything inside the module (functions, macros, callbacks, types):

@moduledoc since: "1.10.0"

For a function, use @doc:

@doc since: "1.13.1"

Erlang

In Erlang's EDoc:

%% @since 0.1.0

The following metadata is available for both modules and functions:

deprecated (binary) - marks a module/function as deprecated, with the given string as the reason.
since (binary) - declares a module/function available from a particular version.

The following metadata is available for modules:

tags (list of atoms) - a list of strings to be added as tags to the module. (Not supported by EDoc.)

Auto-linking

ExDoc for Elixir and Erlang will automatically generate links across modules and functions if you enclose them in backticks.

Elixir

ExDoc will automatically link modules, functions, types or callbacks defined in your project and its dependencies (including Erlang and Elixir). ExDoc will automatically link to it at the dependency's documentation at hexdocs.pm. The link can be configured by setting docs: [deps: [my_dep: "https://path/to/docs/"]] in your mix.exs.

ExDoc supports linking to modules (`MyModule` and `m:MyModule`), functions (`MyModule.function/1`), types (`t:MyModule.type/2`) and callbacks (`c:MyModule.callback/3`). If you want to link a function, type or callback in the current module, you may skip the module name, for example: `function/1`.

You can also use custom text, such as [custom text](`MyModule.function/1`). Link to extra pages using the syntax [Up and running](Up and running.md). The final link will be automatically converted to up-and-running.html.

Link to extra pages in another application using the syntax [Writing Documentation](`e:elixir:writing-documentation.html`), skipping the directory in which the page is. The final link will be automatically converted to https://hexdocs.pm/elixir/writing-documentation.html.

It is also possible to place anchors after the module name and extra pages. For example:

`m:Keyword#module-duplicate-keys-and-ordering` will create a link to https://hexdocs.pm/elixir/Keyword.html#module-duplicate-keys-and-ordering
`e:elixir:syntax-reference.md#expressions` will create a link to https://hexdocs.pm/elixir/syntax-reference.html#expressions

Erlang

ExDoc supports linking to modules (`m:my_module`), functions (`my_module:function/1`), types (`t:my_module:type/2`) and callbacks (`c:my_module:callback/3`). If you want to link a function, type or callback in the current module, you may skip the module name; e.g.: `function/1`.

You can also use custom text, such as [custom text](`my_module:function/1`). This also allows you to refer to Erlang/OTP modules: [The array module](`array`) (note that when a module is given as the link target, it is not necessary nor possible to use the m: prefix).

Link to extra pages using the syntax [Up and running](Up and running.md). The final link will be automatically converted to up-and-running.html.

Link to extra pages in another application using the syntax [Using unicode](`e:stdlib:unicode_usage.html`), skipping the directory in which the page is. The final link will be automatically converted to https://hexdocs.pm/elixir/writing-documentation.html.

It is also possible to place anchors after the module name and extra pages. For example:

`m:argparse#quick-start` will create a link to https://erlang.org/doc/man/argparse#quick-start
`e:stdlib:unicode-usage.md#what-unicode-is` will create a link to https://erlang.org/doc/apps/stdlib/unicode-usage.html#what-unicode-is

Admonition blocks

You may want to draw attention to certain statements by taking them out of the content's flow and labeling them with a priority. Such statements are called admonitions. (They are also known as asides or callouts.) An admonition block is rendered based on the assigned label or class. ExDoc supports warning, error, info, tip and neutral tags, on header levels h3 and h4.

The syntax is as follows:

> #### Error {: .error}
>
> This syntax will render an error block

The result for the previous syntax is:

Error {: .error}

This syntax will render an error block

For example, if you change the class name to neutral, you get the same admonition block in neutral style:

Neutral {: .neutral}

This syntax will render a neutral block

Tabsets

Where only one section of content of a series is likely to apply to the reader, you may wish to define a set of tabs.

This example contains code blocks, separating them into tabs based on language:

Elixir

IO.puts "Hello, world!"

Erlang

io:fwrite("Hello, world!\n").

Tabbed content must be defined between  and  HTML comments. Each h3 heading results in a new tab panel, with its text setting the tab button label.

Here is the above example's source:

<!-- tabs-open -->

### Elixir

```elixir
IO.puts "Hello, world!"
```

### Erlang

```erlang
io:fwrite("Hello, world!\n").
```

<!-- tabs-close -->

Extensions

ExDoc renders Markdown content for you, but you can extend it to render complex objects on the page using JavaScript. To inject custom JavaScript into every page, add this to your configuration:

docs: [
  # ...
  before_closing_head_tag: &before_closing_head_tag/1,
  before_closing_body_tag: &before_closing_body_tag/1
]

# ...

defp before_closing_head_tag(:html) do
  """
  <!-- HTML injected at the end of the <head> element -->
  """
end

defp before_closing_head_tag(:epub), do: ""

defp before_closing_body_tag(:html) do
  """
  <!-- HTML injected at the end of the <body> element -->
  """
end

defp before_closing_body_tag(:epub), do: ""

Besides an anonymous function, you can also pass a module-function-args tuple. It will call the given module and function, with the format prefixed to the arguments:

docs: [
  # ...
  before_closing_head_tag: {MyModule, :before_closing_head_tag, []},
  before_closing_body_tag: {MyModule, :before_closing_body_tag, []}
]

Or you can pass a map where the key is the format:

docs: [
  # ...
  before_closing_head_tag: %{html: "...", epub: "..."},
  before_closing_body_tag: %{html: "...", epub: "..."}
]

Rendering Math

If you write TeX-style math in your Markdown, such as $\sum_{i}^{N} x_i$ , it ends up as raw text on the generated pages. To render expressions, we recommend using KaTeX, a JavaScript library that turns expressions into graphics. To load and trigger KaTeX on every documentation page, we can insert the following HTML:

<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.16.4/dist/katex.min.css" integrity="sha384-vKruj+a13U8yHIkAyGgK1J3ArTLzrFGBbBc0tDp4ad/EyewESeXE/Iv67Aj8gKZ0" crossorigin="anonymous">
<script defer src="https://cdn.jsdelivr.net/npm/katex@0.16.4/dist/katex.min.js" integrity="sha384-PwRUT/YqbnEjkZO0zZxNqcxACrXe+j766U2amXcgMg5457rve2Y7I6ZJSm2A0mS4" crossorigin="anonymous"></script>

<link href="https://cdn.jsdelivr.net/npm/katex-copytex@1.0.2/dist/katex-copytex.min.css" rel="stylesheet" type="text/css">
<script defer src="https://cdn.jsdelivr.net/npm/katex-copytex@1.0.2/dist/katex-copytex.min.js" crossorigin="anonymous"></script>

<script defer src="https://cdn.jsdelivr.net/npm/katex@0.16.4/dist/contrib/auto-render.min.js" integrity="sha384-+VBxd3r6XgURycqtZ117nYw44OOcIax56Z4dCRWbxyPt0Koah1uHoK0o4+/RRE05" crossorigin="anonymous"
  onload="renderMathInElement(document.body, {
    delimiters: [
      {left: '$$', right: '$$', display: true},
      {left: '$', right: '$', display: false},
    ]
  });"></script>
</script>

For more details and configuration options, see the KaTeX Auto-render Extension.

Rendering Vega-Lite plots

Snippets are also objects you may want to render in a special manner. For example, assuming your Markdown includes Vega-Lite specification in vega-lite code snippets:

<script defer src="https://cdn.jsdelivr.net/npm/vega@5.20.2"></script>
<script defer src="https://cdn.jsdelivr.net/npm/vega-lite@5.1.1"></script>
<script defer src="https://cdn.jsdelivr.net/npm/vega-embed@6.18.2"></script>
<script>
  document.addEventListener("DOMContentLoaded", function () {
    for (const codeEl of document.querySelectorAll("pre code.vega-lite")) {
      try {
        const preEl = codeEl.parentElement;
        const spec = JSON.parse(codeEl.textContent);
        const plotEl = document.createElement("div");
        preEl.insertAdjacentElement("afterend", plotEl);
        vegaEmbed(plotEl, spec);
        preEl.remove();
      } catch (error) {
        console.log("Failed to render Vega-Lite plot: " + error)
      }
    }
  });
</script>

For more details and configuration options, see vega/vega-embed.

Rendering Mermaid graphs

Similarly to the example above, if your Markdown includes Mermaid graph specification in mermaid code snippets:

<script>
  function mermaidLoaded() {
    mermaid.initialize({
      startOnLoad: false,
      theme: document.body.className.includes("dark") ? "dark" : "default"
    });
    let id = 0;
    for (const codeEl of document.querySelectorAll("pre code.mermaid")) {
      const preEl = codeEl.parentElement;
      const graphDefinition = codeEl.textContent;
      const graphEl = document.createElement("div");
      const graphId = "mermaid-graph-" + id++;
      mermaid.render(graphId, graphDefinition).then(({svg, bindFunctions}) => {
        graphEl.innerHTML = svg;
        bindFunctions?.(graphEl);
        preEl.insertAdjacentElement("afterend", graphEl);
        preEl.remove();
      });
    }
  }
</script>
<script async src="https://cdn.jsdelivr.net/npm/mermaid@10.2.3/dist/mermaid.min.js" onload="mermaidLoaded();"></script>

For more details and configuration options, see the Mermaid usage docs.

Changing documentation over time

As your project grows, your documentation may very likely change, even structurally. There are a few important things to consider in this regard:

Links to your extras will break if you change or move file names.
Links to your modules, and mix tasks will change if you change their name.
Links to functions are actually links to modules with anchor links. If you change the function name, the link does not break but will leave users at the top of the module's documentation.

Because these docs are static files, the behavior of a missing page will depend on where they are hosted. In particular, hexdocs.pm will show a 404 page.

You can improve the developer experience on everything but function names changing by using the redirects configuration. For example, if you changed the module MyApp.MyModule to MyApp.My.Module and the extra get-started.md to quickstart.md, you can setup the following redirects:

Elixir

For this example, we've changed the module MyApp.MyModule to MyApp.My.Module, and the extra get-started.md to quickstart.md

redirects: %{
  "MyApp.MyModule" => "MyApp.My.Module",
  "get-started" => "quickstart"
}

Erlang

For this example, we've changed the module :my_module to :my_module2, and the extra get-started.md to quickstart.md

{redirects, [
  {"my_module", "my_module2"},
  {"get-started", "quickstart"}
]}.

Contributing

The easiest way to test changes to ExDoc is to locally rebuild the app and its own documentation:

Run mix setup to install all dependencies
Run mix build to generate the docs and open up the generated doc/index.html
(optional) Run npm run --prefix assets build:watch if working on assets for automatic recompilation
Run mix lint to check linting and formatting (and mix fix to automatically fix it)
(important) Do not add the files in the formatters/ directory to your commits, those will be handled by the maintainers

See the README in the assets/ directory for more information on working on the assets.

License

ExDoc source code is released under the Apache 2 License. The generated contents, however, are under different licenses based on projects used to help render HTML, including CSS, JS, and other assets.

Any documentation generated by ExDoc, or any documentation generated by any "Derivative Works" (as specified in the Apache 2 License), must include a direct, readable, and visible link to the ExDoc repository on each rendered material. For HTML pages, every single page is a rendered material. For PDF, EPUB and other ebook formats, the whole body of documentation is a rendered material.