Sellat

sellat-mcp

The official MCP server for SELLAT: ask Claude, Cursor or any MCP client to protect a file, follow its proof, add the qualified eIDAS seal or verify a proof, all from the chat.

"Protect ~/Contracts/draft-v3.pdf with Sellat." "Has the proof of my last photo reached Bitcoin yet?" "Check this file against the evidence package in my Downloads."

Your files never leave your machine. The server runs locally, hashes the file on your computer and sends SELLAT only its SHA-256 (plus the name and size shown on the certificate). It is a thin layer over the sellat-cli client and the sellat-verify offline verifier.

Setup

Claude Desktop: one click

1. Download sellat.mcpb from the latest release and open it. Claude Desktop shows an install dialog; it brings its own Node.js, so there is nothing else to install.
2. Paste your API key when it asks: create a free account at sellat.app, then a key in your dashboard (API keys). Without a key you can still find, fingerprint and verify files.

Then just talk: "protect the contract I downloaded yesterday". Claude finds the file in your Downloads, Desktop, Documents or Pictures folder (whatever they are called on your system) and asks you which one if several fit.

A file you drag into the chat goes to the model, not to this server: say where it is saved instead, or let Claude find it.

Other clients

You need Node.js 18 or later, and the API key as above.

Claude Code

claude mcp add sellat -e SELLAT_API_TOKEN=sellat_… -- npx -y sellat-mcp

Gemini CLI

gemini mcp add -e SELLAT_API_TOKEN=sellat_… sellat npx -y sellat-mcp

Cursor, Claude Desktop without the extension, and other clients (.cursor/mcp.json, claude_desktop_config.json, …):

{
  "mcpServers": {
    "sellat": {
      "command": "npx",
      "args": ["-y", "sellat-mcp"],
      "env": { "SELLAT_API_TOKEN": "sellat_…" }
    }
  }
}

Variable	Default
SELLAT_API_TOKEN	—	your API key (SELLAT_API_KEY is accepted too)
SELLAT_DOWNLOAD_DIR	the system's downloads folder	where certificates and packages are saved
SELLAT_API_URL	https://sellat.app	another SELLAT environment

Tools

Tool	What it does	Key	Network
sellat_find	find a file by name in Downloads, Desktop, Documents and Pictures (localized names included); names only, never contents	no	none
sellat_hash	SHA-256 of a local file	no	none
sellat_stamp	protect a file: hash locally, create the proof; qualified: true adds the qualified eIDAS seal	yes	SELLAT (hash only)
sellat_status	state of a proof: Polygon anchor, Bitcoin, seal, URLs	yes	SELLAT
sellat_list	the account's proofs, newest first	yes	SELLAT
sellat_seal	the qualified timestamp (eIDAS, RFC 3161) for an existing proof; spends one seal	yes	SELLAT
sellat_account	plan, seals left, today's proof budget	yes	SELLAT
sellat_download	save the PDF certificate, the evidence package (ZIP) or the seal's .tsr; never overwrites	yes	SELLAT
sellat_verify	check a file against a proof.json, an evidence .zip or a proof id: Merkle path recomputed locally, anchor checked on a public Polygon node	no	public RPC (and SELLAT only to fetch a proof by id)

Stamping the same file twice returns the first proof (the earlier date is the stronger one), and a retried call never creates a second proof.

Timing

A proof is anchored on Polygon in a Merkle batch: within minutes on the Pro account, at the end of a fixed four-hour UTC slot on the free account (00, 04, 08, 12, 16 and 20 h). Bitcoin, through OpenTimestamps, confirms some hours later. The qualified seal is issued at once. The server tells the model this, so it does not promise a blockchain transaction in seconds.

Payments

Nothing is ever paid through the MCP server. Protecting files is free within the account's daily budget. The qualified seal spends a seal from the account (new accounts get a welcome seal); with none left the tool answers with the link to buy a pack on the website, where the invoice, VAT and withdrawal terms live. The model is told to give you that link and to request a seal only when you asked for one.

What a proof proves

That these exact bytes existed no later than the anchored time, verifiable by anyone without trusting SELLAT. On its own it does not prove authorship or ownership. sellat_verify checks the file, the Merkle path and the Polygon anchor, and reads the anchoring block's time from the chain — the only date it states as proven (a proof whose own date differs fails; offline checks the math and states no date). It does not check the qualified seal's .tsr (any RFC 3161 tool does, e.g. openssl ts -verify).

Develop

npm install
node --test
npm run bundle   # dist/sellat.mcpb, the Claude Desktop extension

Release: bump version in package.json, manifest.json and VERSION in src/server.mjs; npm publish; npm run bundle and attach dist/sellat.mcpb to a GitHub release.

MIT licence.