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A compatibility layer that makes formspec_version 4 (and later) formspecs render more correctly in Minetest 5.3.0 and earlier.

This will work with most mods without any additional configuration. If you want to disable automatic formspec translation, add fs51.disable_monkey_patching = true to minetest.conf.


Minetest 5.1.0 introduced changes to formspecs that made them much less painful to create and work with. However, formspecs are interpreted client-side and to take advantage of these changes you would normally need to force everyone to upgrade Minetest. This mod detects these older clients and modifies formspecs sent to them to try and make sure they are at least usable.

How to use

  1. Install the mod
  2. Hope it works properly and doesn't break anything


FS51 replaces some newer formspec elements with fallbacks if clients don't support them, however this does have some limitations:

  • Animated images will just display their first frame.
  • Fullscreen background colours (the fbgcolor value in bgcolor) don't work.
  • Hypertext elements will lose all formatting and interactivity.
  • Models will just display their underlying texture.
  • Scroll containers are broken.


  • If your mod stores minetest.show_formspec during load time, you'll need to add fs51 as an optional dependency to mod.conf so it can use the patched show_formspec code.
  • If a mod you use has broken node formspecs with fs51 enabled, try adding fs51.disable_meta_override = true to minetest.conf (and please open an issue against fs51).


This mod depends on my formspec_ast library.

API functions

You probably don't need to use these unless you're embedding fs51 outside of Minetest.

  • fs51.backport(tree): Applies backports to a formspec_ast tree and returns the modified tree. This does not modify the existing tree in place.
  • fs51.backport_string(formspec): Similar to formspec_ast.unparse(fs51.backport(formspec_ast.parse(formspec))).

Unlike the automatic backporting, these functions will preserve newer elements such as hypertext and background9 so the formspec will still work properly with newer clients.