The One-Time Password (OTP) Simple Message Service (SMS) Verification API determines the ownership of a mobile device. Users provide the API with a phone number; the engine generates a 6-digit one time password for verification. JSON is the preferred response format. Dark Gray Engines offers user intelligence tools and data mining services. Organizations can benefit from user behavior analysis with advanced machine learning, predictions, credit card fraud detection, address verification, proxy detection, language prediction, and sentiment analysis.