franc is an open-source natural language detection library for JavaScript, available as both an npm package and a CLI tool. It analyzes text input and returns the most likely language as an ISO 639-3 three-letter code. franc supports more languages than any comparable library, with packages available for 82, 187, or all 419 detectable languages depending on the precision needed.

How It Works

franc uses trigram-based statistical analysis derived from the Universal Declaration of Human Rights (UDHR), the most widely translated copyright-free document. The franc() function returns the single most likely language code, while francAll() returns a ranked array of all candidate languages with confidence scores. You can filter results using only and ignore options to constrain detection to specific language sets.

Package Variants

Three npm packages are available: franc-min (82 languages, speakers of 8M+), franc (187 languages, speakers of 1M+), and franc-all (all 414 detectable languages). The CLI is available as franc-cli. All packages are ESM-only and work in Node.js 14.14+, Deno, and modern browsers.

Agent Integration

AI agents can use franc to detect the language of incoming text before routing it to language-specific processing pipelines. The CLI (franc "text to detect") returns a language code directly, making it easy to integrate into shell scripts and automation workflows. In Node.js, agents can import franc programmatically to classify multilingual content, filter datasets by language, or validate that generated text matches the target language. The francAll() function provides confidence-ranked results useful for ambiguous text where multiple languages may be present.

Installation

Install the library: npm install franc. Install the CLI globally: npm install franc-cli --global. The project is licensed under MIT. Documentation and source code are on GitHub.