REST API - Head Tags

This plugin adds all the tags in the <head> section of a site to WordPress REST API responses. You can download it here.
It is perfect if you are using WordPress for a headless set-up and you would like to add the meta tags generated by your WordPress SEO plugin (like Yoast SEO or All-in-One SEO Pack) to the WordPress REST API output.
If you are using Yoast SEO version 14.0 or later, we recommend that you use the @frontity/yoast package instead.
Table of Contents
​Prerequisites​
​Compatibility​
​How to use this plugin​
​Entities with head tags​
​In a Frontity project​
​In a different project​
​Settings​
​Purge cache​
​Enable output​
​Skip cache​
​WordPress installation​
​Troubleshooting​
Prerequisites
This package depends on the PHP DOM library. It looks like not all PHP servers include it by default, so make sure you have it installed before using this plugin.
If you get some errors regarding this dependency have a look a this thread.
Compatibility
This plugin is compatible and works out of the box with the following WordPress SEO plugins:
Yoast SEO
All in One SEO Pack
Are you using a different SEO plugin and want to know if it's compatible? Feel free to ask in the community forum.
How to use this plugin
Entities with head tags
The plugin has been developed to include the head_tags field to the REST API response of most of the WordPress core entities:
Posts, pages, attachments and custom post types
Post types: for archive pages
Categories, tags and custom taxonomies
Authors
In a Frontity project
In this case, you just have to install the @frontity/head-tags package and it'll work automatically.
In a different project
You need to understand better how it works and add the data manually.
How to fetch the head_tags field manually
You have to get each entity from its respective REST API endpoint.
For example, for fetching the posts you should go to /wp-json/wp/v2/posts&id=123 endpoint, for fetching the categories you have to go to wp-json/wp/v2/categories&id=123, and for custom post types or custom taxonomies would be a different URL in each case.
In the case of the homepage, it could be less intuitive and you should go to /wp-json/wp/v2/types/post. As previously said, each entity has a different endpoint so if you aren't familiar with this, you should check the WordPress REST API reference for more info.
Inside each endpoint, it will be a new field named head_tags , which will be an array of objects representing the tags that WordPress would normally include inside the HTML head element. These objects have the properties tag, attributes and content.
For example for these HTML tags:
<title>Hello wordl! - My Site</title>
  <meta name="robots" content="max-snippet:-1, max-image-preview:large, max-video-preview:-1">
  <link rel="canonical" href="<http://mysite.com/hello-world/>" />
This would be the content of the head_tags field:
"head_tags": [
  {
    "tag": "title",
    "content": "Hello world! - My Site"
  },
  {
    "tag": "meta",
    "attributes": {
      "name": "robots",
      "content": "max-snippet:-1, max-image-preview:large, max-video-preview:-1"
    }
  },
  {
    "tag": "link",
    "attributes": {
      "rel": "canonical",
      "href": "<http://mysite.com/hello-world/>"
    }
  }
]
Settings
The settings of this plugin are really simple.
Purge cache
In order to not affect the performance of your web, the head_tags field is cached for all your responses, but we've added a button to purge this cache in case something changes.
Enable output
By default, the head_tags field is included in the common endpoint of each entity. You can configure it so it doesn't appear by default and to be shown when you include the head_tags=true query.
For example, with the output disabled, https://mysite.com/wp-json/wp/v2/posts won't show the head_tags field unless you have the query ? head_tags=true at the end.
Skip cache
In case you want to skip the cache, you can do so by adding to the query the parameter skip_cache.
There are some cache plugins for the REST API that also use the same parameter. In case you want to ignore the cache for the REST API call but not for the head tags, you can use skip_cache&head_tags_skip_cache=false.
WordPress installation
First of all you have to install the plugin. You can do it:
Automatic: from within the WordPress dashboard go to Plugins, click the Add New button, search for REST API - Head Tags (by Frontity) and click Install Now.
Manual: this method requires that you download the plugin and upload it to your web server via FTP.
For a more detailed explanation, WordPress explains how to do this on this guide.
Once installed, you have to activate it and it will be running!
The head_tags field is cached and enabled by default, but you can purge the cache or disable the output as explained in the Settings section above.
Troubleshooting
The REST API returns an HTML response or it shows an error
This could happen with some plugins and themes that add hooks to the wp_head action.
What the REST API - Head Tags plugin does is to call the wp_head action for every entity contained in the REST API response and transform the generated HTML code into a JSON object. That means, any hook registered to that action could be causing the problem if it:
generates invalid HTML
unexpectedly ends the PHP execution
throws an exception
You can check these topics in the community for specific cases that might help you.
NewsPaper theme: REST API - Head Tags Plugin error with NewsPaper theme​
Password Protected plugin: REST API - Head Tags Plugin Breaking with Password Protected​
Another reason why it could return an error is when you make a request to a custom post type endpoint that is not expected to have the head_tags field (like the menu-items endpoint).
The solution is just disable the REST API - Head Tags plugin output when making those requests, simply adding head_tags=false to the query, as explained in REST API - Head Tags plugin not working with WordPress REST API Menus Endpoints.
Missing tags inside head_tags field
One possibility is that the WordPress theme or plugin generates those fields in a different action than wp_head. This is not easy to solve, you would have to find what hooks add the missing fields and attach them to wp_head, or write those hooks yourself.
A known case for this is the NewsPaper theme, wich adds the <title> tag in header.php directly - without using the wp_head action. You can take a look at REST API - Head Tags Plugin error with NewsPaper theme for a specific solution if you are using this theme.
This problem could also happen if there is no theme at all in your WordPress site, because themes are normally what add those tags inside <head>. You can try using one that comes with WordPress by default to fix this.
Also, if you are using a plugin or any other system to cache the REST API responses you can try also clearing the cache.
Unexpected or outdated head_tags field
Try clearing the cache.
Try using skip_cache=true as a parameter in a specific REST API request to regenerate the head_tags field values that appear in the response.