Using https://editor.swagger.io/ I just caught a few errors that so far had gone unnoticed. I had a few routes with path parameters (e.g. get("/dota2/abilities/:dota2_ability_id", Dota2.AbilityController, :show)) but I forgot to declare :dota2_ability_id in the parameters list. Here it is, commented out:

  @spec open_api_operation(atom()) :: Op.t()
  # /dota2/abilities/:dota2_ability_id
  def open_api_operation(:show),
    do: %Op{
    # parameters: [OpenAPI.param(:dota2_ability_id)],
      responses: OpenAPI.resp_Dota2Ability()
    }

Could we add some check that makes the ....OpenAPI.spec() call fail if path parameters are missing?
I'm not sure what could be done for missing parameters of other kinds.