has replaced Project Open Data.

On January 14, 2019, the Foundations for Evidence-Based Policymaking Act ("Evidence Act"), which includes the OPEN Government Data Act, was signed into law. The Evidence Act requires the Office of Management and Budget, the Office of Government Information Services, and the General Services Administration to develop and maintain an online repository ( of tools, best practices, and schema standards to facilitate the adoption of open data practices across the Federal Government.

Archived content of Project Open Data can be accessed at its GitHub repository. You can report missing content or provide any additional feedback via GitHub or by emailing

ISO 8601 Guidance


Term ISO-8601
Decennial R/P10Y
Quadrennial R/P4Y
Annual R/P1Y
Bimonthly R/P2M or R/P0.5M
Semiweekly R/P3.5D
Daily R/P1D
Biweekly R/P2W or R/P0.5W
Semiannual R/P6M
Biennial R/P2Y
Triennial R/P3Y
Three times a week R/P0.33W
Three times a month R/P0.33M
Continuously updated R/PT1S
Monthly R/P1M
Quarterly R/P3M
Semimonthly R/P0.5M
Three times a year R/P4M
Weekly R/P1W
Hourly R/PT1H