The small jobs around an HTML to app conversion
Turning HTML into an app is quick; the details around it are what take the time. Android wants the icon at seven sizes, a package name in a specific syntax, a version code that only rises, a splash icon inside a safe area, and permissions that match what the pages really call. Each is trivial on its own, and each fails a build or a Play submission when wrong — usually after the wait.
These tools do those jobs one at a time, in your browser. Images are resized with the Canvas API, ZIPs are written locally and nothing touches the network, so they keep working offline and you can paste unreleased configs and pages into them safely.
Prefer to skip the pieces? The HTML to App builder takes an HTML file, a ZIP or a URL and returns a signed Android app with the icon set, splash screen and manifest generated for you.