Mirror of https://github.com/modelcontextprotocol/ext-apps — Official repo for spec & SDK of MCP Apps protocol - standard for UIs embedded AI chatbots, served by MCP servers
- TypeScript 76.4%
- MDX 19.3%
- JavaScript 4.3%
| Filename | Latest commit message | Latest commit date |
|---|---|---|
db1b48552b* feat(pdf-server): Interactive PDF viewer example
PDF viewer with PDF.js featuring:
- Chunked binary loading with progress bar
- Text extraction for AI context
- arXiv paper support (fetch by ID)
- Page navigation with keyboard shortcuts
- Zoom controls (including Ctrl+0 reset)
- Fullscreen mode support
- Horizontal swipe for page changes (disabled when zoomed)
- Page persistence in localStorage
- Text selection via PDF.js TextLayer
- Clickable title link to source URL
- Rounded corners and subtle border styling
* chore: Add pdf-server to screenshot generation list
* refactor(pdf-server): Simplify and generalize PDF loading
- Accept any HTTP(s) URLs instead of ArXiv-only
- Use HTTP Range requests for chunked binary loading
- Remove ArXiv-specific code (arxiv.ts, metadata fetching)
- Remove CLAUDE.md index generation
- Flatten hierarchical folder structure to simple entries list
- Remove dead code: getPdfSummary, httpFileSizes
- Simplify base64 encoding using Buffer
- Simplify chunk extraction using slice()
- Consolidate DEFAULT_PDF_URL constant
The server now works with any PDF URL, not just arXiv papers.
HTTP Range requests stream chunks on-demand when supported.
* feat(pdf-server): Include title and selection in model context
- Add pdfTitle to updateModelContext structuredContent
- Include selection position (text, start, end) when text is selected
- Add debounced selectionchange listener to update context on selection
* fix(pdf-server): Restore default URL in view_pdf schema
The UI needs the default value in the schema to show it properly.
* refactor(pdf-server): Further simplifications
- Remove hard-coded test paths from main()
- Remove unused resources: pdfs://metadata/{pdfId}, pdfs://content/{pdfId}
- Remove unused metadata fields: subject, creator, producer, creationDate, modDate
- Remove unused entry fields: relativePath, estimatedTextSize
- Remove filterEntriesByFolder and folder filter from list_pdfs
- Remove redundant output schema validation (trust typed returns)
- Simplify scanDirectory and createLocalEntry signatures
Total: 1836 → 1666 lines (-170 lines, -9%)
* refactor(pdf-server): Major simplification for didactic focus
Simplified the example to focus on key MCP Apps SDK patterns:
- Chunked data through size-limited tool calls
- Model context updates (page text + selection)
- Display modes (fullscreen vs inline)
- External links (openLink)
Changes:
- Remove local file support (HTTP URLs only)
- Restrict dynamic URLs to arxiv.org for security
- Simplify types: url instead of sourcePath/sourceType
- Simplify indexer: 168 → 44 lines
- Simplify loader: 318 → 171 lines
- Simplify server: 337 → 233 lines
- Fix selection text normalization
- Rewrite README with didactic focus
Total: 1836 → 1236 lines (-33%)
* feat(pdf-server): Add file:// URL support for local files
- Local paths are converted to file:// URLs on startup
- file:// URLs must be in the initial list (strict validation)
- Dynamic URLs still restricted to arxiv.org only
- Updated README with local file examples
* fix(pdf-server): Improve selection detection with logging
- Add logging to selectionchange handler to verify it fires
- Add fallback matching without spaces (TextLayer spans may lack spaces)
- Log selection detection success/failure for debugging
The issue: PDF.js TextLayer renders text as positioned spans without
space characters between them. When selecting across spans:
- pageText has spaces (items joined with ' ')
- sel.toString() may not have spaces
- indexOf fails to match
The fix tries exact match first, then falls back to spaceless matching.
* feat(pdf-server): Format model context as markdown with front matter
Model context now looks like:
```markdown
---
url: https://arxiv.org/pdf/...
page: 5/144
---
Page text with <pdf-selection>selected text</pdf-selection> inline.
```
This is cleaner for the model to parse and includes the source URL.
* refactor(pdf-server): Extract smart truncation helpers
Added two well-designed helpers:
formatPageContent(text, maxLength, selection?)
- Centers truncation window around selection if present
- Adds <truncated-content/> markers at elision points
- Wraps selection in <pdf-selection> tags
- Allocates 60% context before, 40% after for readability
findSelectionInText(pageText, selectedText)
- Tries exact match first
- Falls back to spaceless match for TextLayer quirks
- Returns { start, end } or undefined
Example output with selection:
```
<truncated-content/>
...context before... <pdf-selection>selected text</pdf-selection> ...context after...
<truncated-content/>
```
* fix(pdf-server): Truncate inside selection tags when selection too long
When selection is too large for the budget:
<truncated-content/><pdf-selection><truncated-content/>start...end<truncated-content/></pdf-selection><truncated-content/>
This keeps the selection structure intact while showing beginning and end.
* refactor(pdf-server): Remove unused read_pdf_text, use Attention paper as default
- Remove read_pdf_text tool (viewer extracts text client-side with pdfjs)
- Remove PdfTextChunk and ReadPdfTextInput types
- Remove loadPdfTextChunk from pdf-loader
- Change default PDF to 'Attention Is All You Need' (1706.03762)
- Update README with modest language
* refactor(pdf-server): Simplify to use URL as ID, rename view_pdf to display_pdf
Major simplifications:
- Use URL directly as identifier (no hashing)
- Remove displayName - show elided URL with full URL as tooltip
- Rename view_pdf to display_pdf with better description
- Update all references from pdfId to url
- Simplify storage key and model context
The tool description now explains it displays an interactive viewer in the chat.
* feat(pdf-server): Normalize arxiv URLs to PDF format
arxiv.org/abs/... -> arxiv.org/pdf/...
Applied both at startup and when loading dynamic URLs.
* docs(pdf-server): Add prompt engineering to display_pdf description
* fix(pdf-server): Sharp rendering on retina displays
Account for devicePixelRatio when rendering canvas:
- Scale canvas dimensions by dpr
- Scale context by dpr
- Keep CSS size at logical pixels
* fix(pdf-server): Normalize arxiv URLs in read_pdf_bytes too
* add to e2e spec
* add to e2e spec
* add to e2e spec
* add to e2e spec
* regen
* chore: regenerate package-lock.json and fix hono vulnerability
* docs: add pdf-server screenshot to READMEs
* regen
* ci: add missing examples to pkg-pr-new publish
* ci: add pdf-server to npm publish examples
* Update README.md
* pdf-server: improve tool response text for better model context
* revert unrelated screenshot changes
* pdf-server: dynamically add arxiv URLs in read_pdf_bytes
Fixes 'PDF not found' error when server restarts between display_pdf
(which adds the entry) and read_pdf_bytes (which previously only looked
up existing entries). Now read_pdf_bytes mirrors display_pdf's logic
and dynamically adds arxiv URLs to the index.
* cap length of context update in pdf-server
* format
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| .github/workflows | ||
| .husky | ||
| docs | ||
| examples | ||
| plugins/mcp-apps | ||
| scripts | ||
| specification/draft | ||
| src | ||
| tests/e2e | ||
| .gitattributes | ||
| .gitignore | ||
| .prettierignore | ||
| .prettierrc.json | ||
| AGENTS.md | ||
| build.bun.ts | ||
| CLAUDE.md | ||
| CONTRIBUTING.md | ||
| LICENSE | ||
| package-lock.json | ||
| package.json | ||
| playwright.config.ts | ||
| README.md | ||
| RELEASES.md | ||
| tsconfig.json | ||
| typedoc.config.mjs | ||
@modelcontextprotocol/ext-apps
This repo contains the SDK and specification for MCP Apps Extension (SEP-1865).
MCP Apps are a proposed standard inspired by MCP-UI and OpenAI's Apps SDK to allow MCP Servers to display interactive UI elements in conversational MCP clients / chatbots.
How It Works
MCP Apps extend the Model Context Protocol to let servers deliver interactive UIs to MCP hosts. Here's how it works:
- Tool call — The LLM calls a tool on your server
- UI Resource — The tool's definition links to a predeclared
ui://resource containing its HTML interface - Host renders — The host fetches the resource and displays it in a sandboxed iframe
- Bidirectional communication — The host passes tool data to the UI via notifications, and the UI can call other tools through the host
This enables dashboards, forms, visualizations, and other rich experiences inside chat interfaces.
Overview
This SDK serves two audiences:
App Developers
Build interactive UIs that run inside MCP-enabled chat clients.
- SDK for Apps:
@modelcontextprotocol/ext-apps— API Docs - React hooks:
@modelcontextprotocol/ext-apps/react— API Docs
Host Developers
Embed and communicate with MCP Apps in your chat application.
- SDK for Hosts:
@modelcontextprotocol/ext-apps/app-bridge— API Docs
There's no supported host implementation in this repo (beyond the examples/basic-host example).
We have contributed a tentative implementation of hosting / iframing / sandboxing logic to the MCP-UI repository, and expect OSS clients may use it, while other clients might roll their own hosting logic.
Installation
npm install -S @modelcontextprotocol/ext-apps
Or edit your package.json manually:
{
"dependencies": {
"@modelcontextprotocol/ext-apps": "^0.0.1"
}
}
Examples
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| Map | Three.js | ShaderToy |
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| Sheet Music | Wiki Explorer | Cohort Heatmap |
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| Scenario Modeler | Budget Allocator | Customer Segmentation |
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| System Monitor | Transcript | Video Resource |
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| PDF Server |
Starter Templates
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The same app built with different frameworks — pick your favorite! React · Vue · Svelte · Preact · Solid · Vanilla JS |
The examples/ directory contains additional demo apps showcasing real-world use cases.
To run all examples:
npm install
npm start
Then open http://localhost:8080/.