Command-line MessageFormat Compiler

Parses and compiles JSON, YAML and .properties files of MessageFormat strings into an ES module of corresponding hierarchical functions.

This package was previously named messageformat-cli.


npm install --save-dev @messageformat/core @messageformat/cli

If you’re intending to publish a library with external dependencies, you should also include the runtime as a dependency:

npm install @messageformat/runtime


npx messageformat [options] [input]

input should consist of one or more files or directories, unless defined in a configuration file. Directories are recursively scanned for .json, .yaml, .yml and .properties files. With multiple input files, shared parts of the start of their paths are dropped out of the generated module’s structure.


In addition to defining options on the command line, options may also be set in the "messageformat" object in your package.json file, or in a messageformat.rc.{js,json,yaml} configuration file, using the long-form option names as keys. Input files and directories may also be given as an "include" array in a configuration file. Command-line options override configuration files.

Option Short Description
delimiters -d Set of characters by which the file path is split into output object. Default value is ._/ or ._\, depending on the platform.
extensions -e Array or comma-separated list of file extensions to parse as source files. Default: ['.json', '.yaml', '.yml', '.properties']
locale=lc -l The locale(s) lc to include; if multiple, first is default and others are selected by matching message key. If not set or empty, path keys matching any locale code will set the active locale, starting with a default en locale.
options   Options to pass to the MessageFormat constructor via its second argument. On the command line, use dot-notation to set values, e.g. --options.currency=EUR. For custom formatters, string values will be require()’d based on the current working directory.
outfile=of -o Write output to the file of. If unspecified or -, prints to stdout.
simplify -s Simplify the output object structure, by dropping intermediate keys when those keys are shared across all objects at that level, in addition to the default filtering-out of shared keys at the root of the object.


With messages/strings.json, compile it into an ES module using the default English locale:

npx @messageformat/cli messages/strings.json --outfile=messages/en.js

With messages/en.json and messages/fr.json, combine both into an ES module, with the default export’s top-level keys en and fr containing functions that each use the correct language’s pluralization rules:

npx @messageformat/cli messages/ --locale=en,fr --outfile=messages.js

Note: The locale option could be left out here if is known that the data does not include any 2-3 letter keys matching other locales.

Same, but with this configuration in package.json:

  "messageformat": {
    "locale": ["en", "fr"],
    "include": [
    "outfile": "messages.js"
  "scripts": {
    "build:messages": "messageformat"
npm run build:messages