Localization tools
Edit a traditional ICU message and its argument object, then compare the formatted output across numeric boundaries.
Add a plural or selectordinal argument to see boundary values.
Your message and arguments are processed in this browser tab; they are not uploaded.
Plural categories use this browser's Intl data. Its CLDR version varies by browser and may differ from your app runtime.
Result is out of date. Run the test before exporting.
A translation can parse successfully yet choose the wrong plural branch at 0, 11 or 21. This ICU MessageFormat tester runs the message with real argument values and shows those boundary cases beside the normal result.
Use the ICU MessageFormat tester while reviewing a single catalog entry, debugging a missing placeholder, or checking a nested select before release. The preview uses FormatJS and the current browser's Intl data, so compare against your production runtime when exact cross-platform output matters.
Catch the branch that looks fine in one locale and fails in another.
The ICU MessageFormat tester runs 0, 1, 2, 5, 11, 21 and 101 without changing your JSON. An exact =0 branch and a locale's one, few or many category can produce very different sentences; the table shows the actual output for each value.
A placeholder such as {name} must have a matching key in the arguments object. The ICU MessageFormat tester reports missing values and parser errors, while keeping the current message visible for correction. Nested select and plural branches run through the same FormatJS parser and formatter.
Paste one traditional ICU MessageFormat 1 string, or load the plural, select or nested example. The invalid example shows how a missing other branch is reported. MF2 syntax such as {$name} belongs to a different format and is rejected here.
Enter one JSON object with keys that exactly match placeholders, including letter case. Change the BCP 47 locale to see how the same number selects another CLDR plural category. The browser supplies those rules, so its data version can vary.
Choose a plural or ordinal variable and inspect 0, 1, 2, 5, 11, 21 and 101. The table temporarily overrides only that argument. Your original JSON stays intact; copy or download only a result that matches the current inputs.
This ICU MessageFormat tester uses one FormatJS runtime to parse and format the same MF1 message. It supports plural, select, selectordinal, offset, nested branches and basic number formatting instead of guessing with a loose tokenizer.
A plural rules tester is useful only if it shows rendered sentences. Select a numeric argument and inspect seven values, including 11 and 21, with the category and output side by side.
The ICU syntax checker reports parser line and column when available. Invalid JSON, missing variables and unsupported locales have separate messages; an old result cannot be copied after input changes.
The ICU message editor workflow waits for typing to stop. Examples and clear show a replacement preview before changing input, and one undo restores both the prior message and its result.
The ICU MessageFormat tester uses Intl.PluralRules from your current browser. Switch the locale to compare categories and rendered text. A value of 21 can select a different branch from 11 in some languages; exact =n branches are checked before plural categories.
Yes. Put a plural inside a select, or the other way around, and supply every argument needed by the selected path. The nested example demonstrates both. Boundary runs replace only one numeric value so the remaining JSON arguments stay the same.
It tests traditional MF1 through FormatJS, including plural, select, selectordinal, offset and basic number formatting. It does not support MF2, host-rendered rich text, or every ICU4J or ICU4C style. Verify runtime-specific features in the library your app deploys.
Inside a plural option, # inserts the formatted numeric value after any offset. It is not a general placeholder outside plural syntax. Try changing count from 1 to 2 in the default example to see that value in the result.
ICU quoting uses apostrophes for syntax characters in specific contexts. If the parser flags a brace or apostrophe, inspect its line and column and check the FormatJS ICU syntax rules. Do not hide an invalid branch by adding arbitrary backslashes; they may appear literally in output.
Found a message this tester handles differently from your app?
Try the default count example, then change its locale and inspect 11 beside 21.
Keep this ICU MessageFormat tester handy when a translation looks correct for one value but fails on another.
Runs locally in your current browser.