To join multiplayer servers, Eaglercraft uses a custom proxy plugin (for Bungeecord or Velocity) that converts the browser's WebSocket connection into the standard TCP connection used by Minecraft.
Among the chatter was a player called Atlas, who offered a tour. Atlas had a voice that fit the server: a little gravelly, fond of old maps. He led Juno through narrow streets and over a cobblestone bridge to a hill where a single structure stood: an observatory made from stone and glass blocks, lit by a few well-placed torches. Atlas told her it had been held by the same group of players for years, a place where folks came to remember builds they'd made in earlier versions. eaglercraft 1.5.2 link