FileSeal Secure Send

fileseal-send (MCP server)

A standalone Model Context Protocol stdio server that wraps the FileSeal Secure Send API (/v1/sends). It encrypts files client-side (AES-GCM-256) before they ever reach FileSeal and exposes three tools to an MCP client (e.g. Claude).

This package is self-contained: it does not import from the FileSeal Next app. Its crypto (crypto.mjs) mirrors FileSeal's server-side attachment format byte-for-byte (a 12-byte IV followed by AES-GCM ciphertext, with the key base64url-encoded in the link fragment), so that ciphertext it produces decrypts on the FileSeal /receive/[id] page. That page fixes the format: a changed crypto.mjs produces links that will not open.

Tools

• secure_send: encrypt one or more files and create a send.
  • Inputs: filePath, or filePaths (up to 10 files under one link), or (fileBase64 + filename + mimeType), recipientEmail?, deliveryMode ('link' default | 'email'), expiryHours? (1-168, default 48), message?, senderName?.
  • link mode (default, zero-knowledge for the file): the AES key is never sent to FileSeal; the tool returns the full share link with the key in its #k= fragment.
  • email mode: FileSeal emails the recipient a working link and stores the key server-side. Requires recipientEmail. Pass senderName too: without it the email says the files are from "Someone".
  • Not encrypted, in either mode: the file name, senderName and message. FileSeal stores them as plain text and anyone with the link can read them, so keep secrets out of message.
  • Several files: pass them together as filePaths to send them under one link. Calling once per file makes a separate link for each.
  • Limits: up to 10 files per call, 3 MB in total. The files travel inline as base64 in the request body, which is what caps it; FileSeal's own 10 MB per file is not reachable through this tool. Types: PDF, DOC, DOCX, TXT, JPG, PNG.
• send_status: { id } → status, expiry, download count, audit events. Only sends created with the same API key are visible.
• revoke_send: { id } → the link stops working immediately, and FileSeal attempts to delete the encrypted files from its servers.

Environment variables

Running

No install needed: npx fetches and runs the latest published version:

FILESEAL_API_KEY=fsk_... \
FILESEAL_API_BASE_URL=https://fileseal.uk \
npx -y @fileseal/send

The server speaks MCP over stdio, so it's normally launched by an MCP client rather than run by hand.

# from this package's directory
npm install
FILESEAL_API_KEY=fsk_... \
FILESEAL_API_BASE_URL=https://fileseal.uk \
node index.mjs

Wiring into Claude (.mcp.json)

{
  "mcpServers": {
    "fileseal-send": {
      "command": "npx",
      "args": ["-y", "@fileseal/send"],
      "env": {
        "FILESEAL_API_KEY": "fsk_your_api_key_here",
        "FILESEAL_API_BASE_URL": "https://fileseal.uk"
      }
    }
  }
}

The "fileseal-send" key is just the local server label; the npm package is @fileseal/send. To run a local checkout instead, point command/args at your copy of index.mjs.

As a Claude Code plugin

The claude-plugin/ folder packages this server as a Claude Code plugin, with a skill that tells Claude how to use it. The plugin asks for your API key when you enable it and keeps it in secure storage rather than in your settings files. To install it from this repository:

/plugin marketplace add fileseal/mcp-send
/plugin install fileseal@fileseal

It works in Claude Code only. The plugin's README explains why, and lists what it runs and sends.