Convert Java Properties to Extension JSON online
Upload a Java .properties file and download it as Browser extension messages.json. Translation keys, plurals and placeholders are preserved. Free, no account needed.
Pick the source format or let the converter detect it from the file.
Used when the source format holds one language per file. Also used as the source language for XLIFF output.
Choose the format you want to download.
The _locales/xx/messages.json format used by Chrome, Firefox and Edge extensions. Every key holds a message and an optional description for translators.
Need it the other way round? Convert Extension JSON to Java Properties.
From: Java .properties
Key=value resource bundles used by Java, Spring Boot and Kotlin backends. Each language lives in its own messages_xx.properties file next to the default bundle.
Used by: Java, Spring Boot, Kotlin, Thymeleaf. One language per file. Read the Java Properties format guide.
# example comment
user.hello=Hello, {0}
hello.world=Hello World!To: Browser extension messages.json
The _locales/xx/messages.json format used by Chrome, Firefox and Edge extensions. Every key holds a message and an optional description for translators.
Used by: Chrome extensions, Firefox add-ons, Edge extensions. One language per file. Read the Extension JSON format guide.
{
"appName": {
"message": "My Extension",
"description": "The name of the extension"
},
"greeting": {
"message": "Hello, $USER$!",
"description": "Greets the user",
"placeholders": {
"user": {
"content": "$1",
"example": "John"
}
}
}
}How to convert Java Properties to Extension JSON
- Drop your .properties file into the converter above, or paste its content.
- Confirm the language of the file. It is guessed from the file name, for example
de.jsonormessages_pt-BR.properties. - Click Convert. You get one .json file per language.
- Preview the result, copy it or download the files.
What changes between Java Properties and Extension JSON
- Keys, texts, plural forms and placeholders are mapped one to one. Comments and descriptions are kept when both formats support them.
Convert and translate in one place
If you need the Extension JSON file in more languages, the fastest route is a free SimpleLocalize project: import the Java Properties file, add languages, run auto-translation with DeepL, Google Translate, OpenAI, Claude or Gemini, and download the result as Extension JSON. The CLI does the same from CI with upload and download commands, so the conversion becomes part of your build. See also translating Java Properties files.
Frequently asked questions
Is the converter free?
Yes. There is no signup and no limit on the number of conversions beyond a few requests per second.
Are my files stored?
No. The file is parsed in memory, converted and returned in the same request. Nothing is written to disk or a database.
What about plurals and placeholders?
Plural forms are normalized to ICU message syntax and written back in the native form of Extension JSON. Placeholders are kept, and Apple and Android specific syntax is translated between platforms. Read more in the pluralization guide.
Convert Java Properties to other formats
Translate your Extension JSON files
- Import Java Properties or Extension JSON files into a free project
- Auto-translate with DeepL, Google, OpenAI, Claude or Gemini
- Download in any of the supported formats or publish to the CDN