Purpose – This paper aims to examine the relation between the cost of debt and the adoption of eXtensible Business Reporting Language (XBRL). Design/methodology/approach – The financial data are obtained from the Compustat database. Regression analysis is used to examine the research hypotheses. Findings – The authors find that both voluntary and mandatory adoption of XBRL lead to a lower cost of debt for firms, with weak evidence that this reduction is greater for the former than the latter. Research limitations/implications – The findings support the policy of the USA Securities and Exchange Commission (SEC), and thus this paper recommends that adoption of XBRL should be mandatory for all public firms. Practical implications – The findings encourage top managers to develop their firms’ XBRL systems. Originality/value – The results support the SEC’s policy of mandatory XBRL adoption, as it can lead to greater financial reporting transparency and mitigate information asymmetry between management and bondholders.