Paper Download MCP Server

MCP server for downloading academic papers from multiple sources with intelligent routing.

Note: This project is built on top of scihub-cli, adapting its core functionality for MCP integration. If you find this useful, consider starring both projects!

Features

• Multi-Source Support: Downloads from multiple sources with automatic fallback
  • arXiv: Prioritized for preprints (free, no API key needed)
  • Unpaywall: For open access papers (requires email)
  • Direct PDF: Handles direct PDF URLs
  • PMC: PubMed Central articles
  • HTML Landing: Extracts PDF links from article pages
  • Sci-Hub: Fallback for older papers (coverage-driven)
  • CORE: Additional OA fallback
• Intelligent Routing: Priority-based source selection with year-aware routing
• 3 MCP Tools:
  • paper_download - Download single paper by DOI or URL
  • paper_batch_download - Download multiple papers with progress reporting
  • paper_metadata - Get paper metadata without downloading PDF
• Clean Filenames: [YYYY] - Paper Title.pdf format
• Rate Limiting: Built-in delays for API compliance
• Comprehensive Error Messages: Actionable suggestions on failures

Installation

For Users (Recommended)

No manual installation required! Use uvx for automatic environment management:

{
  "mcpServers": {
    "paper-download": {
      "command": "uvx",
      "args": ["paper-download-mcp"],
      "env": {
        "PAPER_DOWNLOAD_EMAIL": "your-email@university.edu"
      }
    }
  }
}

For Developers

git clone <repository-url>
cd paper-download-mcp
uv sync
uv run python -m paper_download_mcp.server

Configuration

Required Environment Variables

• PAPER_DOWNLOAD_EMAIL: Your email address (required for Unpaywall API compliance)
  • Example: researcher@university.edu
  • Used for Unpaywall API tracking and contact purposes

Optional Environment Variables

• PAPER_DOWNLOAD_OUTPUT_DIR: Default output directory (default: ./downloads)

Claude Desktop Setup

Add to your claude_desktop_config.json:

{
  "mcpServers": {
    "paper-download": {
      "command": "uvx",
      "args": ["paper-download-mcp"],
      "env": {
        "PAPER_DOWNLOAD_EMAIL": "your-email@university.edu",
        "PAPER_DOWNLOAD_OUTPUT_DIR": "/path/to/papers"
      }
    }
  }
}

After configuration, restart Claude Desktop.

Tools

paper_download

Download a single academic paper by DOI or URL.

Parameters:

• identifier (required): DOI or URL (e.g., 10.1038/nature12373)
• output_dir (optional): Output directory (default: ./downloads)

Example:

Download the paper 10.1038/nature12373

Returns:

• Markdown with download details (file path, size, source, timing)
• Error message with suggestions if download fails

paper_batch_download

Download multiple papers sequentially with progress reporting.

Parameters:

• identifiers (required): List of DOIs or URLs (1-50 maximum)
• output_dir (optional): Output directory (default: ./downloads)

Example:

Download these papers: 10.1038/nature12373, 10.1126/science.1234567

Returns:

• Markdown summary with statistics
• List of successful downloads
• List of failed downloads with errors

Note: Downloads are sequential with 2-second delays for rate limiting.

paper_metadata

Retrieve paper metadata without downloading the PDF.

Parameters:

• identifier (required): DOI or URL

Example:

Get metadata for 10.1038/nature12373

Returns:

• JSON with paper details:
  • DOI, title, year, authors, journal
  • Open access status
  • Available download sources

How It Works

Intelligent Source Routing

The server uses priority routing to keep fast sources first:

1. arXiv IDs/URLs: Try arXiv first, then OA sources if needed
2. DOIs (year < 2021): OA sources first, Sci-Hub last
3. DOIs (year ≥ 2021): OA sources only (Sci-Hub has no coverage)
4. Year unknown: OA sources first, Sci-Hub last

Download Process

1. Normalize DOI from URL/identifier
2. Detect publication year via Crossref API (DOIs only)
3. Route to appropriate source based on priority/year
4. Download PDF with retry on failure
5. Validate file (PDF header, size check)
6. Generate filename: [YYYY] - Title.pdf
7. Return absolute file path

Rate Limiting

• 2-second delay between batch downloads
• Respects Unpaywall API limits (~100k requests/day)
• Built-in exponential backoff retry (3 attempts max)

Troubleshooting

"PAPER_DOWNLOAD_EMAIL environment variable is required"

Solution: Set the email in your Claude Desktop config (see Configuration section above).

"Paper not found in any source"

Possible causes:

• Invalid or incorrect DOI
• Paper too recent (not yet indexed)
• Paper behind paywall with no open access version
• Sci-Hub mirrors temporarily unavailable

Solutions:

• Verify DOI on doi.org
• Use paper_metadata to check availability
• Try again later (mirrors may recover)

Download times out

Causes:

• Slow network connection
• Sci-Hub mirror selection taking too long
• Large PDF file

Solutions:

• Check internet connection
• Retry (mirror selection is cached after first success)
• Single papers typically complete in <15 seconds

Downloaded file is corrupted

The server validates PDFs before returning. If you encounter corruption:

1. Check disk space
2. Verify file permissions in output directory
3. Try different paper (may be source issue)

Testing

MCP Inspector

Test the server with MCP Inspector:

export PAPER_DOWNLOAD_EMAIL=test@example.com
npx @modelcontextprotocol/inspector uv run python -m paper_download_mcp.server

Unit Tests

uv run pytest

Legal Notice

IMPORTANT: This tool provides access to academic papers through multiple sources:

• Unpaywall (https://unpaywall.org): Legal open-access aggregator operated by OurResearch. Recommended and prioritized when available.

• Sci-Hub: Operates in a legal gray area. While it provides access to research, it may violate copyright laws in some jurisdictions. Use at your own risk.

User Responsibilities:

• You are responsible for compliance with applicable copyright laws in your jurisdiction
• This tool is intended for research and educational purposes only
• The maintainers assume no liability for how you use this tool
• When possible, prefer legal open-access sources (Unpaywall)

By using this tool, you acknowledge these legal considerations and agree to use it responsibly.

Project Structure

paper-download-mcp/
├── src/
│   └── paper_download_mcp/
│       ├── server.py           # FastMCP entry point
│       ├── models.py           # Pydantic input schemas
│       ├── formatters.py       # Markdown/JSON formatters
│       ├── tools/
│       │   ├── download.py     # Download tools
│       │   └── metadata.py     # Metadata tool
│       └── scihub_core/        # Copied from scihub-cli
├── pyproject.toml
├── README.md
└── .gitignore

Architecture

Layer Architecture

1. FastMCP Server Layer: Protocol handling, tool registration, config validation
2. MCP Tools Layer: Request parsing, response formatting, async coordination
3. Models & Formatters: Data validation, output serialization
4. scihub_core Layer: Academic paper logic (unchanged from scihub-cli)

Async Pattern

All tools use asyncio.to_thread() to wrap synchronous scihub-cli code:

@mcp.tool()
async def paper_download(...):
    def _sync_download():
        # Synchronous scihub-cli code
        client = SciHubClient()
        return client.download_paper(doi)

    # Run in thread pool
    result = await asyncio.to_thread(_sync_download)
    return format_result(result)

This preserves the battle-tested scihub-cli code without modifications.

Performance

Operation	Target	Typical	Max
Get Metadata	<1s	0.5s	2s
Single Download	<5s	2-3s	10s
Batch (10 papers)	<40s	25-30s	60s

Note: First download may take longer (5-10s) due to mirror selection. Subsequent downloads use cached mirror.

Contributing

For Maintainers: Syncing from scihub-cli

The scihub_core/ directory contains code copied from the upstream scihub-cli project. When bugs are fixed or features added to scihub-cli:

Workflow:

1. Fix/implement in scihub-cli project first
2. Run tests and commit to scihub-cli
3. Copy updated files to paper-download-mcp/src/paper_download_mcp/scihub_core/
4. Test MCP server functionality
5. Commit with message referencing upstream commit:

   sync: Update <file> from scihub-cli (<description>)
   
   Synced from scihub-cli commit <hash>
   <details of changes>
   

Last sync: scihub-cli@9787efc (2024-12-02) - Fixed year type bug in UnpaywallSource

License

MIT License - See LICENSE file for details

Credits

• Built with FastMCP
• Uses scihub-cli as core download engine
• Metadata from Unpaywall and Crossref

Support

For issues or questions:

1. Check the Troubleshooting section above
2. Open an issue on GitHub (include error messages and steps to reproduce)

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Disclaimer: This tool is provided as-is for research and educational purposes. Users assume all responsibility for compliance with applicable laws and regulations.