Doichain MCP Server

Tamper-evident timestamps for your AI agent.
Prove that a document already existed at a given time: anchor its hash on the Doichain (proof of existence), verify proofs and read names, blocks and addresses.
One URL, no account, no API key, no installation.

Quick start · Tools · How it works · Limits · Security · Tool reference · Self-hosting · Deutsch

Endpoint: https://doi-api.sendlabs.de/mcp · Streamable HTTP · stateless · no authentication required

The Doichain is a public blockchain with a built-in name-value store (a Namecoin descendant, merge-mined with Bitcoin). This server makes it usable for any agent that speaks the Model Context Protocol: Claude, ChatGPT, Cursor, VS Code Copilot and many more. Ask your agent in plain language, it picks the right tool itself:

"Anchor the hash of offer-2026.pdf on the Doichain." "Did this contract already exist before October 1?" "Are d/example or id/alice about to expire?" "How is the Doichain doing right now?"

Opening the endpoint in a browser shows the landing page with setup instructions.

Quick start

Claude Code

claude mcp add --scope user --transport http doichain https://doi-api.sendlabs.de/mcp

Check with claude mcp list. Without --scope user the server only applies to the current project.

Claude (web and desktop)

1. Open Customize → Connectors and click +.
2. Choose Add custom connector, name it Doichain and paste https://doi-api.sendlabs.de/mcp.
3. In a chat, enable it via + → Connectors.

Custom connectors also work on the free plan (one connector). On Team and Enterprise an owner adds it in the organization settings.

ChatGPT

Turn on Settings → Security and login → Developer mode, then create an app under Plugins → + with the URL above and authentication None. Developer mode is available on the web for Plus, Pro, Business, Enterprise and Education.

Cursor

~/.cursor/mcp.json (all projects) or .cursor/mcp.json (one project):

{
  "mcpServers": {
    "doichain": { "url": "https://doi-api.sendlabs.de/mcp" }
  }
}

VS Code (Copilot agent mode)

.vscode/mcp.json:

{
  "servers": {
    "doichain": { "type": "http", "url": "https://doi-api.sendlabs.de/mcp" }
  }
}

Any other client

Try it without an AI client using the MCP Inspector: npx @modelcontextprotocol/inspector, choose Streamable HTTP and enter the URL. A small Python example is in examples/check_proof.py.

Tools

All tools return structured JSON (structuredContent) and carry MCP tool annotations. Only anchor_proof is not read-only. Parameters, return fields and examples: docs/tools.md.

How a proof of existence works

sequenceDiagram
    participant U as You
    participant A as AI agent
    participant M as Doichain MCP server
    participant D as Doichain
    U->>A: "Anchor offer-2026.pdf"
    A->>A: sha256sum offer-2026.pdf (the file never leaves your machine)
    A->>M: anchor_proof(sha256)
    M->>D: name_doi poe/<sha256> = {"v":1,"alg":"sha256",...}
    D-->>M: transaction id (pending)
    M-->>A: txid, verify URL
    Note over D: next block, usually within 10 minutes
    U->>A: "Did this document exist before October 1?"
    A->>M: check_proof(sha256)
    M->>D: name_show / name_history
    M-->>A: confirmed, block 433,335, 2026-09-25 23:21 UTC

Only the hash, and optionally a public note or file name, goes on chain. A SHA-256 cannot be turned back into the document. Anyone can verify a proof later with check_proof or on verifile.it, and changing a single byte of the document produces a different hash.

What a proof shows, and for how long:

• The timestamp is permanent. The anchoring transaction and its block time stay in the blockchain history for good.
• The name is not. poe/<sha256> stays active for 36,000 blocks (about 250 days at ten minutes per block). After that anyone can register it again, with their own note and address. check_proof keeps reporting the first anchoring as the proof time and shows a later registration separately in latest_registration. anchor_proof does not register an expired hash again unless you ask for it with reanchor_expired, and search_names lists expired proofs with include_expired.
• Existence, not authorship. A proof shows that a document with this hash existed no later than the block time. It does not show who submitted it. The hosted endpoint registers the names from the operator's wallet, which pays for them and holds them.

Agents need access to the file to hash it (Claude Code, Cursor, VS Code). In a plain chat, Verifile is the easiest way: drop the file, it is hashed in the browser and anchored with one click.

Limits and quotas

Hosted chat apps (Claude on the web, ChatGPT) connect from their providers' data centers, so all their users share the quota of those addresses. For regular anchoring use a client that connects from your own machine (Claude Code, Cursor, VS Code) or ask DOI Labs for an own key. Anchoring pauses automatically when the operating balance of the node wallet falls below a reserve, reading keeps working.

Security and privacy