

Settings page with code editor and post-ID list.
A minimal way to inject a single inline JavaScript snippet into the <head> of one or more specific posts, pages or products. You give it a comma-separated list of post IDs and the JS body — that is the entire surface area.
The point is the absence of features. There is no per-post UI, no script library, no CDN selector, no “fire on event” toggle. If all you need is to drop a tracking pixel or a tiny script on three specific pages, you do not want a 2 MB plugin that wants to manage your whole site.
Set it up under Settings Lightweight JS snippet. The page provides a textarea for the JS (no <script> tags — those are added for you) and a comma-separated list of post IDs to load it on.