examples[pdf]: limit context length #270
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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
- 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.
- Add pdfTitle to updateModelContext structuredContent - Include selection position (text, start, end) when text is selected - Add debounced selectionchange listener to update context on selection
The UI needs the default value in the schema to show it properly.
- 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%)
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%)
- 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
- 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.
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.
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/>
```
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.
…r 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
…isplay_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.
arxiv.org/abs/... -> arxiv.org/pdf/... Applied both at startup and when loading dynamic URLs.
Account for devicePixelRatio when rendering canvas: - Scale canvas dimensions by dpr - Scale context by dpr - Keep CSS size at logical pixels
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.
antonpk1
previously approved these changes
Jan 14, 2026
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