Show HN: Extend UI – open-source UI kit for modern document apps
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Open-source React UI kit for viewing and editing PDF, DOCX, XLSX, and CSV documents with bounding box citations and e-signatures.
Extend UI provides React components for rendering multiple document formats including PDF, DOCX, XLSX, and CSV. Features include viewers with bounding box citations (highlighting specific content with source references), file upload, e-signature support, a schema builder, file system browser, and document split functionality. The XLSX viewer uses a custom Rust parser ported to WebAssembly. Components use react-virtual to virtualize pages for performance and support zoom (with rotation support in progress). The kit targets user-facing flows, AI agents, and internal tools.
What commenters are saying
Commenters raised performance concerns about the demo site, with reports of significant lag on MacBook Pro models during scrolling and component interaction. Several users requested web components instead of React-only, citing framework exclusivity, though the team noted React familiarity guided their initial choice. The file system component lacks features like search, sorting by date/size/type, and page navigation in viewers. Users praised the bounding box citation handling and XLSX rendering approach. A few noted missing React/Next.js clarity in marketing materials; the team acknowledged this and added clarification. Real-world feedback: one user indicated server-side PDF conversion was their previous workaround; another mentioned using Rust parsers (calamine for XLSX) for data extraction but needed rendering, making this useful.