Modern YAML does not use a reaction: field next to choices or actions. Visible buttons are declared with button:, and typed commands with command: or alias:.

choices:
  - command: north
    button: "Go north"
    to: north_room

global_aliases:
  back: "Home"
  help: "Help"

rooms:
  - id: corridor
    choices:
      - command: back
        to: home

actions:
  - verb: inspect
    target: still
    alias: still
    if: ~
    text_ok: "The still waits for your ingredients."

The player can type still instead of inspect still.

actions:
  - verb: use
    target: potion
    button: "Drink potion"
    if: "potion"
    do: "hp.+.10"
    text_ok: "+10 HP!"

events:
  - if: ~
    button: "Meditate"
    do: "mana.+.5"
    text: "+5 mana."