Extend UI
shadcn registry of PDF, DOCX, XLSX and CSV viewers with bounding-box citations
Extend UI is the internal component layer Extend uses for document-heavy products, released as a 55-item shadcn registry under the @extend namespace. Beyond a standard shadcn base (button, dialog, sidebar, command, sonner and the rest) it ships the parts nobody else open-sources: PDF, DOCX, XLSX, PPTX and CSV viewers, DOCX and Excel editors, bounding-box citation overlays, layout blocks, a file-system browser, file upload with thumbnails, e-signature, document splits, and a schema builder. Components land as editable source, not a dependency. Built for teams putting a document agent or a review queue in front of users.
npx shadcn@latest add @extend/pdf-viewerThis is the first thing to reach for when a build needs a document viewer with citation highlighting — writing bounding-box overlays on top of react-pdf by hand costs days, and @extend/bounding-box-citations plus @extend/pdf-viewer gets there in one CLI call. It is a shadcn superset, so install it into a project that already ran shadcn init or the base ui primitives will collide with yours; prefer the block variants (`*-block`) when you want a whole working screen rather than a bare viewer. Do not use it for a generic app UI — the base primitives are only there to support the document parts.
Why it is here. Document viewers with grounded citation overlays are the missing layer in every RAG and document-agent demo, and this is a production set from a company that runs it over millions of pages, given away MIT.
- PDF, DOCX, XLSX, PPTX and CSV viewers
- bounding-box citation overlays
- e-signature and schema builder
- 8 ready-made block screens
- MIT, from production use at Extend
Verified 2026-08-15. HTTP 200. https://ui.extend.ai/, https://ui.extend.ai/r/registry.json (parsed, 55 items enumerated: 44 registry:ui, 8 registry:block, 1 lib, 1 hook, 1 component), https://www.extend.ai/ui, https://github.com/extend-hq/ui, GitHub API repos/extend-hq/ui. https://extend-ui.com/ui/docs/components 404s — the live docs path is www.extend.ai/ui/docs/components.
