Convert ARB to Extension JSON online
Upload a Flutter ARB 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 ARB.
From: Flutter ARB
Application Resource Bundle files are JSON documents with ICU message syntax and optional @metadata entries. Flutter's gen_l10n tool turns them into typed Dart localization classes.
Used by: Flutter, Dart intl, gen_l10n. One language per file. Read the ARB format guide.
{
"@@locale": "en",
"hello.world": "Hello World!",
"@hello.world": {
"description": "Hello world message"
}
"my_address": "Address",
}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 ARB to Extension JSON
- Drop your .arb 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 ARB 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 ARB 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 ARB 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 ARB to other formats
Translate your Extension JSON files
- Import ARB 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