This paper presents an authoring tool for building location-based mobile games, enhanced with augmented reality capabilities. These games are a subclass of pervasive games in which the gameplay evolves and progresses according to player's location. We have conducted a literature review on authoring tools and pervasive games to (i) collect the common scenarios of current location-based mobile games, and (ii) features of authoring tools for these games. Additionally, we have also used the focus groups methodology to find new scenarios for location-based mobile games, in particular regarding how augmented reality can be used in these games. Both literature review and focus groups provide us a set of requirements to design a software architecture for our authoring tool, a web-based application where games are created and executed. In our approach, games are designed as a set of missions that can be ordered or not. Players use mobile devices to perform these missions in order to complete each game. Our main objective is to provide a software solution to enable non-programmers users to design, build and run location-based mobile games. In order to evaluate our tool, we present a game design called "Battle for Fortaleza", and how this game is implemented in our solution.