Edit a plain HTML site in the browser, with no build step

None of the three. PortBay serves the folder itself at a .test hostname with trusted HTTPS, and there is nothing to instrument because nothing is compiled. On a framework project PortBay has to add a source coordinate to the dev server it launches so an element can be traced back through the build; on a static site the browser is already showing you the file. Your folder is byte-identical before and after — the only files PortBay changes are the ones you deliberately edit.

The URL says so. A request for /about/ resolves to about/index.html under the doc root, /contact.html to contact.html, and paths containing .. or anything that is not .html or .htm are rejected outright. That file is searched first and it is trusted precisely because it is the exact document the browser rendered — no other candidate can be the source of what you clicked. Other HTML files under the doc root are searched only after it, so a shared phrase in a second page cannot win over the page you are actually on.

Structural editing is where static HTML is at its strongest, with one caveat worth stating: structural editing is not one of the four write lanes PortBay's cross-stack parity test guards, so treat it as less hardened than text, attributes, classes and page settings. What makes it work well here is anchoring. A structural edit has to pin an element exactly, and the tiers that do it without a coordinate are a unique id in your source — HTML's own uniqueness contract, which cannot go stale the way a coordinate can — and the element's position among same-tag siblings, trusted only when the count in the browser exactly matches the count in the file. On a templated stack a loop breaks that count constantly. On a static page nothing loops, so the counts agree. The one structural operation that is refused outright is extracting an element into a component: on a .html page there is no component file to extract into, and PortBay says so by name rather than inventing a convention.

Yes, straight into the head of the file. A plain HTML document has no router and no runtime head assembly — the title, the meta description, the canonical link and the Open Graph tags are elements in the file, so the panel reads them from there and writes them back there. This is one of the stacks where all four write lanes work: text, attributes, classes and page settings. The cross-stack parity test drives all four against a real static fixture and every one of them writes.

PortBay refuses to write into it, deliberately. A directory named dist, build, out, _site, public, .next, .output, .svelte-kit, .astro, .vercel or target is build output, and a change written there is erased by the next build — persistence that looks real and is not. If you have a generator, the file to edit is its source template — Hugo, Jekyll and Eleventy are each recognised as their own stack, with edits resolved against their layouts rather than their output. This page is about a site whose .html files are the thing you actually wrote.

Not necessarily. A static project can carry content bindings: an attribute on the element names a collection and a field, either for the element's text or for one of its attributes, and PortBay fills those elements in the page it serves so the canvas shows what a visitor would see. A generate step then writes one output file per record with the values in it as real content. Both halves run on the server side on purpose — a client-side fill would keep the words out of the HTML and therefore out of the index. And the element keeps real content between its tags, so a file that has never been through a generate is a working page rather than a broken one.

PortBay's visual editor is a Pro feature, in early access behind an opt-in toggle in Settings, and it is not compiled into the open-source build at all. It attaches to local .test hosts only, and it refuses outright while a project is shared over a public tunnel — the edit bar never applies to tunneled traffic, so you stop the share first. It is also one live page at one breakpoint at a time rather than a multi-frame infinite canvas. Serving your site over HTTPS at its own hostname is in the free, open-source app.