Developer reference

The provider seam#

A provider is a small object: it takes a prompt and returns text, or throws. Which one is used is a setting, and adding one is a registration rather than a patch.

<?php
// PLACEHOLDER — interface name, method signature and action name are not final.
add_action( 'subset_content_builder_register_providers', function ( $registry ) {
	$registry->add( 'local-llama', new My_Local_Llama_Provider() );
} );

The interface stays deliberately narrow. Streaming, function calling and tool use are all things a provider might support and the editor does not ask for, because the editor’s job is “put text in this block” and every capability the interface grows is a capability every provider then has to implement or stub.

Filtering the prompt#

Everything sent to a provider passes through one filter. That is intentional: one place to audit, one place to redact, one place to add a house style.

<?php
// PLACEHOLDER — filter name and context shape are not final.
add_filter(
	'subset_content_builder_prompt',
	function ( string $prompt, array $context ): string {
		// Never let a draft mention a competitor by name.
		return $prompt . "\n\nDo not name any company other than ours.";
	},
	10,
	2
);

Where generated content lives#

Generations are WordPress revisions, which means they are revision post-type rows parented to the post, and every existing revision API works on them.

<?php
// This part is not a placeholder: it is the WordPress API, and it works today.
$revisions = wp_get_post_revisions( $post_id );

A meta key marking which revisions came from a generation (placeholder — not final) is planned, so that an editorial workflow plugin can tell a generated draft from a human edit. Until it exists, the two are indistinguishable, which is worth knowing if you are building a review queue.

What will deliberately not be extensible#

There is no hook that publishes a post. Generation produces a draft revision and stops. An action that skips the editor is the one request we will refuse, because the whole premise of the plugin is that a person reads the thing before it goes out.

Hosted credits are not a provider you can register. The Pro add-on’s hosted generation runs against our own account with our own bill attached, and the seam for it is not a public one.

The free version’s promise, in code terms#

Worth stating precisely, because “free forever” is a claim that needs a mechanism behind it: the free plugin makes requests from your server to your provider using your key. There is no call to any subset.dev endpoint in a generation path, no telemetry attached to a prompt, and no licence check gating a generation. If you find one, that is a bug and a serious one — please open an issue.

github.com/function-form/subset/issues (opens in a new tab)