Properties
Java's key=value answer to INI.
Where it came from
Java introduced .properties in the mid-90s as its built-in configuration store, shipped with the JDK's java.util.Properties. It became the default for localization bundles (messages_en.properties) and app config across the ecosystem.
Frameworks from Spring to Maven still read it. Despite newer formats, properties files remain the lowest-common-denominator config in the JVM world.
How it works
Syntax is key=value (or key:value, whitespace allowed). Lines starting with # or ! are comments. Keys are often dotted namespaces: db.url, db.user.
The historical gotcha: the classic format escaped non-ASCII as \uXXXX (ISO-8859-1), so raw UTF-8 broke. UWC parses the structure and maps dotted keys into a nested JSON object, in your browser.
Convert Properties
Properties → nested JSON, or flatten JSON back — parsed locally with no upload.