NearPlayer

Is a client-side mod that allows you to detect the nearest players on the server.

It displays the name of the nearest player, the distance in blocks, icons of their equipment (armor slots, as well as main hand and off-hand slots), and direction arrows to all nearby players on the screen.

You can configure the mod directly in the game by pressing the "H" key (by default). In the settings, you can specify the radius (it may be limited by the server); if you're playing with a friend but don't want the mod to react to them — enter their nickname in the player exclusion field. Also in the settings, you can enable or disable direction arrows and equipment display.