I tried to include this code in my plug-in php files as well as in functions.php. (In the end I would like it to be in the plug-in's php file but I'm not yet sure if possible, that would probably be the topic of another question.)

It is a very basic method for now, I'm just trying to get a response with some content.

In both cases, I get a 404 response.

add_action( 'rest_api_init', function () {
  register_rest_route( plugin_dir_url(__DIR__).'my-project/api/v1/form', '/action', array(
    'methods' => 'GET, POST',
    'callback' => 'api_method',
  ) );

function api_method($data) {
    return 'API method end.';

And I tried to access URLs (in brower or with AJAX)

I guess I'm missing something.

  • Rest API endpoints live at /wp-json, to include plugin_dir_url in your endpoint registration is extremely unusual, I would strongly recommend against REST endpoint URLs in the plugins folder ( mostly because that's not how the API works, you can't have those kinds of URLs ) – Tom J Nowell Apr 10 at 15:07
  • @TomJNowell – Can you see why this question got so many views in such a short time? Should I ask this on Meta? – leymannx Apr 10 at 21:40
  • asking on meta is a good idea, I'm not sure how we can see views though. Maybe your question was well written and popular? :) – Tom J Nowell Apr 11 at 9:20

Maybe start with just GET. Your route looks weird as well. Try just:

register_rest_route('my-project/v1', '/action/', [
  'methods'  => WP_REST_Server::READABLE,
  'callback' => 'api_method',

And your callback is not returning a valid response. Let your callback look more like this:

$data = [ 'foo' => 'bar' ];

$response = new WP_REST_Response($data, 200);

// Set headers.
$response->set_headers([ 'Cache-Control' => 'must-revalidate, no-cache, no-store, private' ]);

return $response;

Finally you must combine wp-json, the namespace my-project/v1 and your route action to the URL you now can check for what you get:

  • I just followed what you suggested, tried my-domain.local/my-project/v1 , my-domain.local/my-project/v1/get (with and without trailing slashes), still getting 404 response. At the moment, the code is in functions.php. – TTT Apr 10 at 15:02
  • @TTT – It must be my-domain.local/wp-json/my-project/v1/action as you've specified /action/ to be your route. – leymannx Apr 10 at 15:12
  • 1
    Thank you, this worked. Well since the answer is in the comment, I not sure if I should check the answer as solution right away. Also, I can make this return something else than JSON, right ? (I mean not like XML, like php processed HTML code.) ... Then the URL would still contain "wp-json". Weird ... or is there another type of API? – TTT Apr 10 at 15:17
  • 2
    @TTT you can store HTML in JSON as a string then JSON decode in the browser – Tom J Nowell Apr 10 at 15:20
  • 1
    I just found and tested this way here that looks cleaned than including HTML in JSON: gist.github.com/petenelson/6dc1a405a6e7627b4834 – TTT Apr 10 at 16:01

Here's your problem:

register_rest_route( plugin_dir_url(__DIR__).'my-project/api/v1/form', '/action', array(

Specifically the idea that this is possible:


This is extremely unusual, and runs counter to what's in the docs, handbook, and tutorials.

REST API endpoints live at the REST API, which lives at the URL returned by rest_url(). They live at yoursite.com/wp-json. An endpoint is not a full URL path, or an independent API disconnected from the main API.

Instead, you need to define your endpoint names in terms of namespaces and endpoints, and visit the correct URL as described in the REST API's discovery mechanisms.

If we use this:

register_rest_route( plugin_dir_url(__DIR__).'my-project/api/v1/form', '/action', array(

Then we would expect this:


That URL is quite long, and has a number of problems:

  • The first parameter is a namespace, not a URL
  • it's not possible to correctly separate out v1 of the API from v2 due to the way that that /form component has been put in the first parameter, not the second. The first parameter is a namespace, the second a route
  • /action is /action, it doesn't get swapped out for GET OR POST

There are also problems with the callback function:

function api_method($data) {

An endpoint needs to return its data, it cannot output it directly as var_dump would, otherwise the returned data is invalid JSON.

Finally, the methods parameter is incorrect:

'methods' => 'GET, POST',

methods doesn't take a comma separated list, no docs suggest doing this either. Instead, use the predefined values provided by the REST API such as WP_REST_Server::READABLE or WP_REST_Server::ALLMETHODS, these are all mentioned in the handbook and the official documentation for register_rest_route.

A better route to register would be:

    register_rest_route( 'my-project/form/v1', '/action', array(

Giving us:


Notice how I removed the plugin URL and the redundant /api fragment ( it's obvious it's an API already )

  • 1
    Thank you for detailed explanation. I've already marked an answer that came quicker as solution however. – TTT Apr 10 at 15:25
  • You can change your mind about which answer is best, but eitherway think of the site as a wiki, there can be more than 1 good answer – Tom J Nowell Apr 10 at 17:21
  • 1
    One reason why I don't want to change answer is that I have conretely tested and applied the answer I selected as solution. Your answer brought more details and things I had thought in a wrong way somehow, but I haven't litteraly tested and checked it all. I also think that on most StackExchange sites, first good answers get selected, next one get votes. And though this has me scratching my head a bit, I see no reason to remove the solution rewards from the person who solved it first. – TTT Apr 10 at 17:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.