JingJin AI is a native-level American English writing API designed for developers, writers, and cross-border sellers. ✅ Grammar Check: Instantly fix errors with authentic corrections ✅ Polishing: Refine sentences to sound natural & fluent ✅ Multi-tone Rewrite: Adjust formality (formal, casual, academic) ✅ Style Check: Get formality & professionalism scores ✅ Fast & Reliable: Built on top-tier AI models for production use