SDK · CLI · MCP
The three surfaces of Veto Checkout — the @veto-protocol/checkout SDK, the veto CLI, and the MCP server that lets an agent buy from any protocol-speaking merchant.
Veto Checkout ships three surfaces. All are zero-runtime-dependency and run on Node ≥ 22.6.
SDK — createCheckout
@veto-protocol/checkout. The one call a merchant makes, plus the public API barrel.
HTTP adapters
Mount the checkout on node:http, Express, Hono, or Next.js — one line each.
CLI
@veto-protocol/cli. Login, then drive any merchant: discover, catalog, quote, pay,
verify.
MCP server
@veto-protocol/mcp. The buyer-side flow as MCP tools for Claude / Cursor / Continue.
Install the SDK
npm install @veto-protocol/checkoutThe package entry re-exports everything you need — createCheckout, the policy presets
(STRICT / BALANCED / OPEN), the rails (x402Rail / mockRail), the REASON
registry, receipt verification, and the crypto helpers.
Webhooks
Register an endpoint, and Veto POSTs you a signed event on every sale — order.accepted, order.settled, order.rejected, order.held. HMAC-SHA256 signed with a per-endpoint whsec_ secret, at-least-once, retried on a 7-step backoff. Fulfill on order.settled.
createCheckout()
The SDK's front door. Resolves a sparse merchant config into a fully-defaulted checkout handle whose methods map 1:1 to the wire endpoints and MCP tools.