Countersign MCP server

Countersign

A neutral, cross-vendor control plane for AI agents that spend money. Countersign holds the policy, the freeze, and the audit ledger across multiple agent-wallet backends at once — the one thing no single wallet vendor can do, because each only governs its own rail. That aggregation is the moat.

Live version of this loop: countersign.network/demo.html · 60s video

One falsifiable test defines it: **can Countersign freeze agents across many backends at once, in

under a second, with a unified tamper-evident ledger of every attempt? Proven LIVE across four

rails (Coinbase, Turnkey, Openfort, and a Lithic Visa card**) in ~432ms on testnet.

❄️ The hosted Core is paused (2026-09-18). app.countersign.network is switched off: it issues no

keys and existing keys no longer authenticate. These packages are unaffected — they are Apache-2.0,

still published on npm, and work against a Core you run yourself. Point COUNTERSIGN_URL at your own

instance wherever this README says app.countersign.network.

This repository is the open-core front door — the Apache-2.0 packages you build against: the integration contract, the typed client, the MCP tools, and the x402 guard. The control-plane "brain" (the policy compiler, the hash-chained ledger, the vendor adapters, and the hosted Core) is separate and proprietary; you reach it over the network via the SDK/MCP. It was hosted at app.countersign.network, which is currently paused — self-host the Core to use these packages today.

Quickstart

Drop the kill switch + spend guard into any MCP client (Claude, Cursor, …) — one line:

// claude / cursor mcp config
{ "mcpServers": { "countersign": {
  "command": "npx", "args": ["-y", "@countersign/mcp"],
  "env": { "COUNTERSIGN_URL": "https://app.countersign.network", "COUNTERSIGN_API_KEY": "csk_…" }
}}}

Or wire it into your own agent with the SDK:

import { CountersignClient } from "@countersign/sdk";
const cs = new CountersignClient({ baseUrl, apiKey });

await cs.evaluate({ agentId, amount, asset, venue }); // may this spend happen? (allow / deny / needs_approval)
await cs.freeze();                                     // the kill switch — every backend, < 1s

~~Get a free testnet key at app.countersign.network/start~~ — the hosted signup is paused. Run your own Core and issue yourself a key with POST /signup.

Agents paying agents? See examples/guarded-payee — the A2A/AP2 pattern where a payee advertises it is governed and the payer verifies that (and guards its own payment) before any mandate is signed.

Packages (this repo — all Apache-2.0)

Shortened. The full README is on GitHub.