How to add TLD to search exception in Safari

Question

How can I add .locahost to the list of TLDs that Safari will load — instead of searching — without supplying a protocol? Alternatively (or perhaps additionally), how do I get Safari to stop removing the http:// protocol from the URL?

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I've been using project.localhost to handle local development for a while, now that .dev is no longer a viable development TLD. But I'm getting frustrated with Safari's default behavior. What I'd like to do is prevent Safari from submitting the domain name to the search engine.

Desired:

1. enter project.localhost into address bar
2. browser loads http://project.localhost

I would be satisfied with Safari not removing the http:// in the address bar, but I can't find a way to do that, either.

What actually happens:

1. enter project.localhost into address bar
2. browser sends project.localhost to Duck Duck Go
3. user is tempted to test the ballistic properties of keyboard

Or, after I've loaded http://project.localhost and then try to add something after the current URL:

1. click in address bar, URL has been shortened to project.localhost
2. add /test.html to end
3. browser sends project.localhost/test.html to Duck Duck Go
4. user considers software violence

Answer 1

Turns out that the Safari extension might be a long term solution. At this moment, I can't manage the developer membership cost. But here's the working code, for Future Me and anyone else looking into this.

In the extension's global page <script>:

(function() {
    safari.application.addEventListener("beforeSearch", function(event) {
        if (event.query.split("/")[0].split(".").pop() == "localhost") {
            event.preventDefault();
            safari.application.activeBrowserWindow.activeTab.url = "http://" + event.query;
        }
    }, true);
})();