I18n Tools

MCP server for querying and managing JSON translation files. Designed for AI agents (Claude Code, Cursor, etc.) to read and write i18n, i18next, react-i18next, and next-i18next translations directly through the Model Context Protocol.

Supports flat ({locale}.json) and namespaced ({locale}/{namespace}.json) directory layouts with dot-notation keys.

Install

Ask your AI agent:

Install the i18n-tools-mcp MCP server. The translations directory is at ./messages and the base locale is nl.

Or add it manually to your MCP client config (e.g. .claude/settings.json):

{
  "mcpServers": {
    "i18n-tools": {
      "command": "npx",
      "args": ["i18n-tools-mcp", "./messages", "nl"]
    }
  }
}

Arguments:

1. Required: Path to the directory containing your translation files
2. Optional: Base locale code (default: nl) — used in tool descriptions to guide AI agents
3. Optional: JSON indentation spaces (default: 4)

Directory structures

Both flat and namespaced layouts are auto-detected.

Flat — one JSON file per locale:

messages/
  en.json
  nl.json

Namespaced — subdirectory per locale, one JSON file per namespace (i18next-style):

messages/
  en/
    common.json
    auth.json
  nl/
    common.json
    auth.json

In namespace mode, prefix keys with the namespace: common:Users.name. Read operations (query, list, search, missing) work across all namespaces when no prefix is given. Write operations (set, add) require a namespace prefix.

Tools

query

Look up a translation key across all locale files. Returns the value for each locale that has the key.

Parameter	Type	Required	Description
key	string	yes	Dot-notation key, e.g. "Users.name" or "common:Users.name"

set

Set a translation value for a single locale. Creates intermediate keys if needed.

Parameter	Type	Required	Description
locale	string	yes	Locale code, e.g. "nl" or "en"
key	string	yes	Dot-notation key, e.g. "Users.name" or "common:Users.name"
value	string	yes	The translation value

add

Add a translation key to multiple locales at once.

Parameter	Type	Required	Description
key	string	yes	Dot-notation key, e.g. "Users.name" or "common:Users.name"
translations	Record<string, string>	yes	Locale-to-value mapping, e.g. {"nl": "Naam", "en": "Name"}

delete

Delete a translation key from all locale files.

Parameter	Type	Required	Description
key	string	yes	Dot-notation key, e.g. "Users.name" or "common:Users.name"

rename

Rename a translation key across all locale files. Preserves values.

Parameter	Type	Required	Description
oldKey	string	yes	Current dot-notation key, e.g. "Users.name"
newKey	string	yes	New dot-notation key, e.g. "Users.fullName"

move

Move a translation key to a different path across all locale files.

Parameter	Type	Required	Description
oldKey	string	yes	Current dot-notation key, e.g. "Users.name"
newKey	string	yes	New dot-notation key, e.g. "Profile.name"

list

List all translation keys. Optionally filter by a key prefix.

Parameter	Type	Required	Description
prefix	string	no	Key prefix to filter by, e.g. "Users" or "common:"

search

Search translations by value (case-insensitive).

Parameter	Type	Required	Description
value	string	yes	Text to search for in translation values

missing

Find translation keys that exist in some locales but are missing in others. Takes no parameters.

batch

Apply multiple mutations in a single call. Each affected locale file is read once, mutated in memory, and written exactly once — regardless of how many ops touch it. Per-file atomic: if any op fails, no files are written.

Prefer this over repeated set/add/delete/rename/move calls for bulk changes. It minimizes file-watcher churn (Next.js dev, Vite HMR) and avoids partial writes.

Parameter	Type	Required	Description
ops	BatchOp[]	yes	Ordered list of operations (see below)

Each op is one of:

{ "op": "set",    "locale": "en", "key": "Users.name", "value": "Name" }
{ "op": "add",    "key": "Users.email", "translations": { "nl": "E-mail", "en": "Email" } }
{ "op": "delete", "key": "Users.legacy" }
{ "op": "rename", "oldKey": "Users.name", "newKey": "Users.fullName" }
{ "op": "move",   "oldKey": "Users.name", "newKey": "Profile.name" }

Development

pnpm install       # Install dependencies
pnpm dev           # Watch mode
pnpm test          # Run tests
pnpm test:watch    # Watch mode tests
pnpm build         # Compile TypeScript