http://backname.io/

Every IP address has its Backname(tm).

  * 142.250.147.138.backname.io
    resolves to 142.250.147.138

    IPv4 with dots
  * 127-0-0-1.backname.io
    resolves to 127.0.0.1

    IPv4 with hyphens
  * 2a00.1450.401b.810.0.0.0.200e.backname.io
    resolves to 2a00:1450:401b:810::200e

    IPv6 with dots*
  * 0--1.backname.io
    resolves to ::1

    IPv6 with hyphens*

Backname is an open-source project.
This is a public service by Michael Matloka.