Extend UI

Extend UI is an open-source React component library built and maintained by Extend AI for teams building modern document processing products. It started as the internal component layer for Extend's own platform and was released publicly after the team found existing file viewer and document component libraries insufficient for production document-heavy workflows. The library is MIT licensed and distributed through the shadcn component registry.

What It Is

Extend UI is a set of 14 open-source React components and example blocks designed specifically for document agents, review surfaces, and file-management interfaces. Rather than wrapping a generic viewer library, each component is purpose-built for document-processing use cases: PDF, DOCX, and XLSX viewers, bounding box citations, file upload, file thumbnails, e-signature, document splitting, layout blocks, and a Finder-style file browser. Components are installed as editable source code via the shadcn CLI, making them fully customizable and compatible with any existing design system.

Architecture and Installation Model

Components are distributed through the shadcn component registry under the @extend/* namespace. Installing a component copies its source directly into the project, so teams can adapt it to their app's design system without forking a package. Shared primitives like Button, Select, Dialog, ScrollArea, and Tooltip are expected to come from the consuming app's existing component library. The registry namespace is @extend/* and installation uses the standard npx shadcn@latest add command.

Key Components

• PDF / DOCX / XLSX Viewers — Render common document formats inline
• Layout Blocks — Inspect OCR and layout output with selectable blocks, confidence scores, markdown text, and PDF overlays
• Bounding Box Citations — Review extracted values against source PDFs with field-level citations, editable form controls, JSON diffing, and page overlays
• File System — A Finder-style file browser supporting icon, list, column, and gallery views with viewer dialogs for PDF, DOCX, XLSX, and image files
• E-Signature — Capture signatures within document flows
• File Upload / Thumbnails — Handle file ingestion and preview surfaces

Production Lineage

According to the project README, Extend UI components are maintained in production at Extend and are used across workflows that process millions of pages, with fixes and improvements flowing back into the open-source project. The repository was created in May 2026 and had accumulated 932 stars and 51 forks by mid-June 2026, indicating early community traction.

Who It's For

Extend UI targets developers building document-heavy products — internal tools, agent review surfaces, or user-facing document flows — who need polished, production-tested building blocks without starting from a generic viewer. The README notes it works well with design-system agents and prototyping tools that need editable React and Tailwind code, making it relevant for both human developers and AI-assisted coding workflows.