Send files securely from your app or AI agent
Deliver a file to a person as a one-time, encrypted, auto-deleting download link, over a REST API and an MCP server. UK-hosted, with an audit trail and a zero-knowledge option.
What the Secure Send API does
AI agents and backends increasingly produce sensitive files: contracts, KYC extracts, medical letters, financial summaries. Dropping them into chat or a plain email is not safe, and a raw presigned URL has no expiry, no one-time access and no audit. FileSeal gives you a secure egress channel in one request.
Encrypted
AES-GCM-256. In the default link mode the key never reaches FileSeal, so it stores ciphertext it cannot read.
One-time + expiring
The link opens once, then the file is deleted from FileSeal's servers. Set an expiry from 1 to 168 hours.
Logged + UK-hosted
Every send and collection is logged. Hosted in the UK (London), designed for UK GDPR.
MCP-native
Agents call it as a tool via the fileseal-send MCP server. No glue code.
The same API key can also ask a client for documents: create a one-time upload request, let FileSeal email the client or send the link yourself, and poll until the files have arrived. You collect them in the FileSeal dashboard. Upload requests in the docs
Send a file in one request
Encrypt the file on your side, then create the send. In link mode you relay the returned#k= link to the recipient and FileSeal never receives the key.
REST
curl -X POST https://fileseal.uk/v1/sends \
-H "Authorization: Bearer $FILESEAL_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"deliveryMode": "link",
"files": [{
"filename": "contract.pdf",
"mimeType": "application/pdf",
"ciphertextBase64": "<AES-GCM ciphertext, base64>"
}]
}'MCP server (.mcp.json)
{
"mcpServers": {
"fileseal-send": {
"command": "npx",
"args": ["-y", "@fileseal/send"],
"env": {
"FILESEAL_API_KEY": "${FILESEAL_API_KEY}",
"FILESEAL_API_BASE_URL": "https://fileseal.uk"
}
}
}
}Then your agent calls the secure_send tool; it encrypts locally and returns the share link.
Using Claude Code? Install it as a plugin instead: /plugin marketplace add fileseal/mcp-send, then /plugin install fileseal@fileseal. How the plugin works.
Encryption and the zero-knowledge option
Default: link / zero-knowledge (most private)
The AES key lives only in the link’s #k=fragment, which browsers never send to the server, so FileSeal stores ciphertext it cannot read. You relay the link to the recipient.
Opt-in: email delivery
Pass deliveryMode: "email" and FileSeal holds the key so it can email the recipient a working one-time link. Encrypted and safe from outsiders, not zero-knowledge from FileSeal.
Start sending in minutes
Create an account, generate an API key in Settings, and make your first secure send. Free to evaluate.