A formspec library that automatically positions and sizes elements

GUI API / Library

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How do I install this?

An experimental layout manager and formspec API replacement for Minetest. Vaguely inspired by Flutter and GTK.

Online tutorial/demo (source)



  • No manual positioning of elements.
  • Automatic layouting using HBox and VBox containers
  • Some elements have an automatic size.
  • The size of elements can optionally expand to fit larger spaces

Other features

  • No form names. Form names are still used internally, however they are hidden from the API.
  • No having to worry about state.
  • Values of fields, scrollbars, checkboxes, etc are remembered when redrawing a form and are automatically applied.
  • Has an inspector mod to help with developing and debugging forms.


  • This mod doesn't support all of the features that regular formspecs do.
  • FS51 is required if you want to have full support for Minetest 5.3 and below.

Basic example

See example.lua for a more comprehensive example which demonstrates how layouting and alignment works.

-- GUI elements are accessible with flow.widgets. Using
-- `local gui = flow.widgets` is recommended to reduce typing.
local gui = flow.widgets

-- GUIs are created with flow.make_gui(build_func).
local my_gui = flow.make_gui(function(player, ctx)
    -- The build function should return a GUI element such as gui.VBox.
    -- `ctx` can be used to store context. `ctx.form` is reserved for storing
    -- the state of elements in the form. For example, you can use
    -- `ctx.form.my_checkbox` to check whether `my_checkbox` is checked. Note
    -- that ctx.form.element may be nil instead of its default value.

    -- This function may be called at any time by flow.

    -- gui.VBox is a "container element" added by this mod.
    return gui.VBox {
        gui.Label {label = "Here is a dropdown:"},
        gui.Dropdown {
            -- The value of this dropdown will be accessible from ctx.form.my_dropdown
            name = "my_dropdown",
            items = {'First item', 'Second item', 'Third item'},
            index_event = true,
        gui.Button {
            label = "Get dropdown index",
            on_event = function(player, ctx)
                -- flow should guarantee that `ctx.form.my_dropdown` exists, even if the client doesn't send my_dropdown to the server.
                local selected_idx = ctx.form.my_dropdown
                minetest.chat_send_player(player:get_player_name(), "You have selected item #" .. selected_idx .. "!")

-- Show the GUI to player as an interactive form
-- Note that `player` is a player object and not a player name.

-- Close the form

-- Alternatively, the GUI can be shown as a non-interactive HUD (requires
-- hud_fs to be installed).

Other formspec libraries/utilities

These utilities likely aren't compatible with flow.

  • fs_layout is another mod library that does automatic formspec element positioning.
  • fslib is a small mod library that lets you build formspec strings.
  • Just_Visiting's formspec editor is a Minetest (sub)game that lets you edit formspecs and preview them as you go
  • kuto is a formspec library that has some extra widgets/components and has a callback API. Some automatic sizing can be done for buttons. It may be possible to use kuto's components with flow somehow as they both use formspec_ast internally.
  • My web-based formspec editor lets you add elements and drag+drop them, however it doesn't support all formspec features.


See the README file on GitHub or GitLab for more documentation.



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