Versioning and change policy

DayAPI versions live in the path: /v1/. Inside a version, changes are additive only. Breaking changes get a new version and a 12-month overlap.

What counts as additive

• A new response field.
• A new optional parameter.
• A new country added to the covered set.
• A new error code for a case that previously returned a generic error.

What counts as breaking

• Removing or renaming a field or endpoint.
• Changing a field type or a date format.
• Changing a counting rule inside an existing endpoint without a new version.

How changes get announced

Dataset corrections ship without a version change because the old answer was factually wrong. They are listed in a dated change note per country. API shape changes are announced at least 90 days before the old version stops answering, on this site and on the status page. A deprecated version keeps answering for 12 months after its successor launches.