Abstract Budget transparency innovations bring new extent and forms of transparency. The aim of the article is to explore the diffusion of budget explorers, that is, a budget transparency innovation extremely popular in the Czech Republic, and to evaluate their impact on voluntary budget information disclosed. Careful mapping of the diffusion using a survey of budget explores in 72 former Czech district towns and media analysis shows that the key success factor was its convenience for politicians, as it is attractive, easy to implement and up-to-date demonstration of their transparency. Budget explorers are nowadays a standard extension to accounting software, and their usage is evaluated in several government transparency competitions. The major benefit of the budget explorers is that they made for the first time publicly available detailed public financial information, changed the standard of best practice and drew some public attention. At the same time, they, unfortunately, narrowed the scope of the budget transparency debate by omitting the importance of the draft budget and introduction of performance measurement.