Explainpaper is a web application that processes uploaded PDF research papers through a large language model (LLM) pipeline, extracting full document context to power three core features: in-context highlight explanations, a paper-scoped chat interface, and auto-generated structural insights. The system is context-aware, meaning explanations and answers are grounded in the specific paper's content rather than general world knowledge. The Pro tier upgrades the underlying model to a more capable LLM, enables full-paper summarization, and persists highlights and explanations across sessions.