Expose a headless checkout API that accepts structured input (cart items, shipping address, shipping method selection, promo code) in a single or small number of API calls rather than requiring multi-step web form navigation.
Return machine-readable error responses: use structured error objects with a machine-readable code (e.g., INVALID_ADDRESS, PROMO_EXPIRED, ITEM_OUT_OF_STOCK) alongside a human-readable message so agents can handle errors programmatically.
Support idempotency keys on order creation endpoints; document the key header name and behavior clearly so agents can safely retry on network failure without creating duplicate orders.
Provide a checkout session URL that a human can open in a browser to complete payment; this URL should restore the cart state and pre-fill shipping details already collected by the agent, minimizing human steps.
Emit order confirmation data as a structured response (not just a confirmation email) including order ID, itemized summary, total, estimated delivery date, and a tracking info endpoint URL.
Publish your checkout API's OpenAPI spec and/or MCP tool schema so agents can discover and use it without relying on documentation written for human developers.
Known gotchas
Many legacy checkout implementations are tightly coupled to browser session state and cookies; decoupling them for API access may require significant backend refactoring — prioritize the cart creation and checkout session URL endpoints as a minimum viable agent-friendly surface.
Avoid requiring agents to execute JavaScript challenges or solve CAPTCHAs during checkout; these are appropriate bot-detection mechanisms for unidentified scrapers, not authenticated API clients with valid API keys.
Agent-initiated orders may arrive in bursts (e.g., from a multi-merchant order splitting agent); ensure your inventory reservation and order creation endpoints handle concurrent requests without overselling limited-stock items.
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp