An i18next JSON editor that keeps your nesting

Validation runs when the project loads and again after every edit. i18next is one of the two formats where both the ICU and the plural checks apply. The same checks run from the terminal with stringlane check, and over MCP for a coding agent.

• Missing or empty per language

  The key exists in your base language and is absent or blank in another file. i18next falls back at run time, so the string still renders, in the wrong language, and nothing in your build says so.

  missing_key

• Interpolation mismatch

  {{variable}} names are compared as a set rather than by count, so a translation that renamed {{name}} to {{nombre}} is flagged, and so is one that dropped it entirely. Renaming an interpolation variable is the failure that reaches production, because the JSON stays valid.

  format_placeholder_mismatch

• Plural coverage against CLDR

  Keys ending in a CLDR suffix are grouped into one row, and each language is checked against the categories it actually requires. Ukrainian needs one, few, many and other. English needs two. Ship the English pair for Ukrainian and the gap is flagged. Suffix matching is case insensitive, so keys left in an older casing by earlier tooling are still recognised. Ordinal keys such as place_ordinal_one and place_ordinal_two are checked against the language’s ordinal forms (1st, 2nd, 3rd in English), not its ordinary plural forms. A language that holds its own plural forms under a base value with {{count}} has each form checked against that value.

  missing_key

• A count with no plural forms

  i18next uses a key’s _one and _other forms only when they exist, so a base value like {{count}} genres with no plural forms in any language reads “1 genres”, and Russian reads “1 жанров”. It is flagged once, on the base language. A label that shows the number apart from the words, such as Found: {{count}}, is not. stringlane pluralize, the MCP pluralize_key tool and the app’s Add plural forms dialog write the base forms for you.

  count_without_plural

• Invalid ICU

  If you use ICU messages through i18next-icu, they are parsed and validated: unmatched braces, a plural missing other, a malformed select. Unlike Flutter, the i18next ICU runtime does substitute #, so a bare # is left alone here rather than flagged.

  icu_parse_error

• Same as base, and guarded words

  A value identical to the base language usually means it was copied rather than translated. Terms you mark as guarded are flagged when a language changes them instead.

  untranslatedguarded_word_violation