Nice, looks like you're off to a great start.
Here are some features I love about Pinboard.in that you could consider adding to Webtag as it grows:
- iOS/Android share extension, so I can easily bookmark anything from my mobile device. This is crucial for me as the friction is reduced enough that I will actually bookmark things and helps me keep everything in one place.
- Auto-complete tags, boy is this handy.
- Use AI to guess tags that I can easily add with a click. See this browser extension for an example: https://chromewebstore.google.com/detail/pinboard-plus/mphdp...
- A description field that will auto-populate with my highlighted text or default to the site's metadata description. This helps a lot for finding things again without having to stuff a lot of text in an unwieldy title. In the search, I can vaguely describe what I'm looking for and often find it again.
- Semantic search. Pinboard doesn't have this but it could become the holy grail of bookmarking services by adding it. So often I have moments where I recall something I read years ago, but cannot remember the exact wording or how to find it again in a verbatim search function.
- Archival of bookmarks. Even merely automatically submitting the page to an archival site would suffice. The bookmark app I wrote uses a headless browser to save an MHTML file plus yt-dlp to fetch media, but it doesn't have the above features so I don't use it, ha.
- Server-side rendering. The little loading animation is just enough to make the site feel slow and almost defeats your goal of a dead-simple UI. Edit: Also I am seeing 600-700ms response times on the bookmarks endpoint.
For your homepage, I would recommend adjusting the wording on "Plain-text-based bookmarking. No fancy images or graphics." Coming from Pinboard, I was unsure what this meant exactly. At first I wondered if the service archived only the text of bookmarked pages like a "reader mode" feature, especially with the "no limits on storage" note. Also it's not literally plain-text in the typical sense (e.g. .txt files or plain-text accounting). It's just a clean UI. Maybe say "Simple text-only UI" or similar.
On the logged-in menu, I would change "Home" to "My Bookmarks" or similar.
It might be helpful to communicate to prospective users how you plan to fund the project long-term. When selecting a bookmarking service, reliability and longevity are going to be top factors. Free forever, no business plan, etc do not inspire that kind of confidence.
Overall, it's a great start. I wish you luck!