SnappierFrames

Makes item frames actually touch the block they’re hanging on.

Do I need it on the server?

No, but it is recommended. With only the client, item frames will still snap to their supporting blocks. However, the server will still see the frames in their original positions. This could cause incompatibilities with anticheats or unexpected behavior when interacting with the frames as the server would think that you are not looking at the item frame.

What does it do?

A visual explanation is best here.

Without SnappierFrames

With SnappierFrames

SnappierFrames dynamically calculates the edges of a block’s model and correctly adjusts item frames based on it. This allows SnappierFrames to be fully compatible with mods despite not knowing about them.