Introduction

LangSync is CLI tooling for localization workflows in TypeScript applications. Use it to initialize config, validate locale files, sync missing keys, run AI translation for empty values, and handle Excel import/export when needed.

It runs locally, in CI, and in scripts, so your translation maintenance follows the same repeatable flow as application code.

Why LangSync

• Typed configuration. Author langsync.config.ts with full IntelliSense via the defineConfig helper.
• Workflow-first quality checks. Report missing, extra, and empty keys with CI-friendly exit codes.
• Excel round-trip when needed. Export all locales into one workbook, then import safely with structure and keys preserved.
• AI-assisted translation. Fill empty values with langsync translate. OpenAI and DeepL are released; Anthropic and Gemini are available behind the experimental flag.
• Watch mode. Keep locales in sync as you type with langsync watch: incremental sync plus validation on every save.
• Framework integrations. Auto-detects i18next, ngx-translate, and react-intl from your package.json.
• Editor integration. A VS Code extension surfaces missing, extra, and empty keys as native diagnostics while you work.
• CLI output designed for automation. Interactive prompts for local use and machine-readable output when needed (--reporter json).
• Migration path included. Move from i18n-excel-manager with command mapping and setup guidance in one dedicated page.

How it fits in your stack

┌──────────────────┐         ┌──────────────────┐         ┌──────────────────┐
│  src/i18n/       │ ◄────►  │   LangSync CLI   │ ◄────►  │  translations.   │
│  ├ en.json       │         │  validate / sync │         │  xlsx (handoff)  │
│  ├ de.json       │         │  export / import │         └──────────────────┘
│  └ fr.json       │         └──────────────────┘
└──────────────────┘                    ▲
                                        │
                            ┌──────────────────┐
                            │ langsync.config  │
                            │ .ts (typed)      │
                            └──────────────────┘

You keep authoring locale JSON files exactly how your framework expects them. LangSync sits on top as the workflow layer for validation, synchronization, translation, and collaboration handoffs.

Where to go next

• Getting Started — 5-minute walkthrough from zero to validated locales.
• Installation — install with pnpm, npm, or yarn.
• Configuration — every option, every file format.
• Migration from i18n-excel-manager — move existing workflows to LangSync with minimal disruption.
• CLI Reference — init, validate, sync, find-missing, translate, watch, export excel, import excel.
• Integrations — recipes for i18next, ngx-translate, and react-intl.
• VS Code Extension — in-editor diagnostics for missing, extra, and empty keys.
• SDK — drive LangSync workflows in-process from Node.js with @mariokreitz/langsync-sdk.