For agent builders
An MCP server for e-signatures
Signathing runs a remote Model Context Protocol server at signathing.com/api/mcp. Add it to Claude, ChatGPT, Cursor, Claude Code, Grok or any MCP client and your agent gains ten tools: send a PDF to up to 25 signers, check status, remind, void, send from a template, read the account balance, pull the evidence package, and look up any verification code. The first 100 documents a month are free with no card.
What the tools do
send_document takes a PDF by https URL or base64, a title, the signers, and optionally placed fields, and returns the document with each signer's private link. get_document and list_documents report status and who has viewed or signed. remind_document and void_document do what they say. list_templates and send_from_template reuse a template you saved on the website. get_account reports the balance and how many free documents remain this month.
get_evidence returns the evidence package for a document: hashes of the original and signed PDFs, every event with its position in the public evidence log, and the recipe to verify it. verify_signature_code looks up the code stamped beside any Signathing signature, on any document, not only yours.
Connecting it
Hosted clients such as Claude.ai, ChatGPT and the Grok apps take the URL as a custom connector and send you to signathing.com to sign in and approve; the consent screen names the app, the permissions and the host it returns you to. Claude Code, Cursor, VS Code and Windsurf take the same URL with an API key as a bearer header. Clients that only speak stdio can use the open-source bridge in the signathing-mcp repository on GitHub. Exact config blocks for each client are on the developers page.
What a careful agent does after sending
Sending is the easy half. A contract an agent produced is only as good as what can be proven about it later, and an agent should not be the one vouching for its own work. After the document completes, the agent calls get_evidence, recomputes the hashes and chain entries in the package, confirms each entry is in the public log, and resolves the verification code. The agent loop example at signathing.com/verifier/agent-loop.mjs does all of that in one run with no dependencies, and the verifier script can be handed to anyone who wants to repeat it.
Why it is a third party at all
An agent could sign things itself, or stamp its own log. On the day a signature is disputed, the party that controlled the signing system is the party with something to gain. Signathing is nobody's party to the contract, and it does not ask to be trusted either: each signing event is appended to one public hash chain, each day is sealed, archived with the Internet Archive and timestamped on Bitcoin through OpenTimestamps, and the verifier recomputes it all from the package.
Common questions
- Does the signer need an MCP client or an account?
- No. The signer gets a normal private link by email or text and signs in a browser. Only the sender's agent uses MCP.
- Which clients work?
- Any MCP client that speaks Streamable HTTP with OAuth or a bearer header, which includes Claude.ai, ChatGPT, Claude Code, Cursor, VS Code, Windsurf and the Grok apps. A stdio bridge covers the rest.
- What does it cost?
- 100 documents a month free, no card. Then $0.06 a document, falling with volume, from a prepaid balance.
- Can another agent verify a document mine sent?
- Yes. The evidence package and the public log are enough; the verifier needs no account and no key.
Model Context Protocol is an open standard. Client names are the trademarks of their owners and are used only to say where the server connects.
Free, and not the kind of free with a catch
Unlimited documents, up to 25 signers each, certified PDFs on every one. No trial clock and no card to start.
Start signing free