Convert Multi-language JSON to Extension JSON online
Upload a Multi-language JSON 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.
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 Multi-language JSON.
From: Multi-language JSON
A single JSON file where every translation key holds an object with one entry per language. Handy for small projects, static sites and CDN delivery because all languages travel together.
Used by: custom i18n setups, static site generators, CDN delivery. All languages in one file. Read the Multi-language JSON format guide.
{
"en_US": {
"hello.world": "Hello World!",
"my_address": "My address"
},
"pl_PL": {
"hello.world": "Witaj Świecie!",
"my_address": "Mój adres"
}
}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 Multi-language JSON to Extension JSON
- Drop your .json file into the converter above, or paste its content.
- Click Convert. You get one .json file per language.
- Preview the result, copy it or download the files.
What changes between Multi-language JSON and Extension JSON
- Multi-language JSON holds every language in one file, so the converter writes one Extension JSON file per language found in the source.
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 Multi-language JSON 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 Multi-language JSON 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 Multi-language JSON to other formats
Translate your Extension JSON files
- Import Multi-language JSON 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