In June 2018, the SEC adopted Inline eXtensible Business Reporting Language (iXBRL), which embeds XBRL data into HTML-formatted annual reports to improve the accessibility and usefulness of the information disclosures to investors. This study assesses the effectiveness of iXBRL by examining its impact on informational efficiency and information asymmetry. Using a sample that includes iXBRL voluntary adopters before 2019, we find that iXBRL adoption lowers stock return drift and facilitates information being impounded into firm stock prices following the filing of annual reports. We also find that unlike XBRL, iXBRL reduces information asymmetry in the long run. These findings are consistent with the SEC’s intention of adopting iXBRL to combine human-readable and machine-readable information. Our study provides initial evidence on the effectiveness of iXBRL in communicating information to the external users of annual reports.