I've been using Shaarli[1] for the past 15 years, and I'm very happy with it. The code base is small and stable enough (the official version hasn't got a single update over the past 12 years, even though the author is still using it daily[2]) you can easily tweak it to your tastes.

[1]: https://github.com/sebsauvage/Shaarli

[2]: https://sebsauvage.net/links/