Congressional Budget Justification Transparency Act of 2021 This act requires federal agencies to post budget justification materials on certain public websites, including a single searchable website (e.g., USAspending.gov) and each agency's website. The materials most be posted in an open format that enables users to download individual reports, all reports in bulk, and the results of a search. In addition, the materials must be posted no later than two weeks after they are first submitted to Congress. The act also requires the Office of Management and Budget to maintain a public website that includes details regarding the materials, including a list of the agencies that submit budget justification materials to Congress, the dates that the materials were submitted to Congress and posted online, and links to the materials.