.properties

What is a .properties file?

Properties files are simple key-value configuration files used in Java applications and Android development.

Safe format
Type Data
By Sun Microsystems (now Oracle)
MIME text/x-java-properties

Drop any file to identify it

No upload. No signup. No sending your file halfway across the internet.
We tell you what it is, right here in your browser.

What is it

Java Properties files are perhaps the most boring file format in existence, which is exactly what makes them useful. Each line is a key=value pair. Comments start with # or !. That's the entire specification. No nesting, no types, no sections — just strings mapped to strings.

The format is the standard configuration mechanism for Java applications, Android projects, and JVM-based frameworks. Spring Boot's application.properties, Gradle's gradle.properties, and Android's local.properties are daily encounters for millions of developers. Internationalisation (i18n) in Java uses .properties files for translated strings.

Any text editor opens .properties files. IntelliJ IDEA and Eclipse provide syntax highlighting and key-completion for known property names. The format's simplicity means it's trivially parseable in any language, not just Java — Python, JavaScript, and Ruby all have properties file parsers.

Technical details
Full Name
Java Properties File
MIME Type
text/x-java-properties
Developer
Sun Microsystems (now Oracle)
Magic Bytes
N/A
Safety
.properties is a known, safe format. Plain text file. No executable content. May contain passwords or API keys — treat as potentially sensitive.
What opens it
Any text editor
FREE Windows / Mac / Linux
IntelliJ IDEA
FREE Windows / Mac / Linux
VS Code
FREE Windows / Mac / Linux
FAQ
What's the format of a .properties file?
Each line is key=value (or key:value or key value). Comments start with # or !. Values are strings — no numbers, booleans, or nested structures. It's intentionally simple.
Can .properties files contain sensitive data?
Yes — they frequently contain database passwords, API keys, and connection strings. Never commit .properties files with secrets to version control. Use environment variables or a secrets manager instead.
Related formats