The live demo and its two rails
The storefront runs on a Cloudflare Worker at trailhead-shop.postoaklabs.workers.dev and the full source is public at github.com/PostOakLabs/paypal-agent-shop (MIT). Everything runs on PayPal sandbox money: approve anything, click everything, then read the receipts in the sandbox business account's activity.
Trailhead storefront demo
Avo, the storefront's AI agent, runs the whole sale on the PayPal sandbox: selling from the catalog, quoting the pay-in-4 arithmetic, creating and capturing orders, and answering post-purchase questions such as where an order is.
PayPal Agent Shop walkthrough
The five-minute guided tour of the same live demo, with copy-paste commands for the health check, the machine-readable catalog, and the storefront's MCP tools/list call, plus the two-ledger story of the storefront and PayPal's hosted MCP server.
Storefront over MCP
The same storefront speaks MCP at its /mcp endpoint. Catalog search and order reads answer any MCP client; order creation and refunds require an operator bearer token and fail closed without one, so this rail is read-only for visitors. The MCP rail and the browser rail are separate demos: an order created over MCP cannot be captured from the storefront's browser session.
The estate's agentic-payments tooling
These browser tools and ChainGraph nodes already run on this site, and each one sharpens the same platform question the demo answers: what does an agent need before it can safely move money. The developer tools below are the full tool set of the Agentic Commerce & MCP Developer Hub; the nodes are the calculators and validators the site's computation rail serves over MCP.
MCP Tool-Definition Linter & Annotation Designer
Lint a tool definition against JSON Schema 2020-12 and the current naming, output-schema, and annotation rules, then design a consistent annotation set.
Open tool →MCP server.json Validator & Skeleton Generator
Validate a server.json against the 2025-12-11 schema and registry rules, then scaffold a compliant skeleton.
Open tool →Agentic Payments Protocol Comparator & Field Crosswalk
Put AP2, ACP, x402, Visa TAP, and Mastercard Agent Pay side by side across credential, signing, scope, rail, and audit, with a crosswalk and scenario recommender.
Open tool →x402 Header Decoder & Payload Linter with 402 Flow Simulator
Decode x402 headers, lint an exact-scheme PaymentPayload, walk the HTTP-402 verify and settle flow, and check the scheme by network matrix.
Open tool →MCP OAuth 2.1 Authorization Auditor
Validate RFC 9728 protected-resource-metadata, visualize the discovery chain, and check RFC 8707 audience binding for token passthrough risks.
Open tool →RFC 9421 Signature Decoder & Web Bot Auth Readiness
Decode and validate HTTP Message Signatures, lint a Web Bot Auth JWKS directory, and score agent readiness on the substrate under Visa's Trusted Agent Protocol.
Open tool →MCP Spec-Revision Compliance Scorer & Stateless Migration Advisor
Score a server against a target MCP revision and get a breaking-change advisor for the stateless protocol core.
Open tool →ACP Checkout Validator & Shared Payment Token Scope Linter
Validate an ACP checkout-session object and lint a Shared Payment Token for single-use, merchant-bound, amount-capped, short-lived safety.
Open tool →MCP Tool-Poisoning & Prompt-Injection Manifest Scanner
Scan a tool description for poisoning and injection smells: instruction overrides, hidden unicode, role-play framing, tool shadowing, exfiltration hints.
Open tool →A2A Agent Card Validator & Extension Checker
Validate an Agent2Agent agent-card.json against the v1.0 shape, check signed-card signatures, and confirm AP2 and x402 extension declarations.
Open tool →MCP Transport & DNS-Rebinding Security Auditor
Audit Streamable HTTP for Origin and Host validation, loopback binding, DNS-rebinding protection, and token passthrough.
Open tool →Google AP2 Checkout/Payment Mandate (VDC) Builder & Validator
Build and validate Google's AP2 Checkout and Payment Mandate Verifiable Digital Credentials, the external Google and FIDO specification.
Open tool →Visa Trusted Agent Protocol Signature Inspector & Readiness
Parse a Visa TAP signature, surface the agent-recognition signature and replay-protection parameters, and score TAP readiness on RFC 9421.
Open tool →Visa Trusted Agent Protocol Header Verifier
Run a fixed 9-point TAP header check: component coverage, full RFC 9421 signature-base reconstruction, algorithm allowlist, and optional WebCrypto verification.
Open tool →Visa VIC Agent Token Scope & Spend Control Policy Builder
Build and validate agent-scoped payment credentials: agent identity binding, MCC merchant scope, per-transaction and aggregate spend limits, stablecoin rail permissions.
Open tool →Visa Agentic Ready Program Issuer & Processor Readiness Scorer
Score an issuer or processor across all six Visa Agentic Ready certification pillars, from agent token issuance to stablecoin settlement.
Open tool →Mastercard Agent Pay: Agentic Token Scope & Consent-Policy Builder
Build and lint a Mastercard Agentic Token scope: agent identity, merchant scope, and consent policy covering limit, merchants, expiry, and velocity.
Open tool →MCP Developer Readiness Scorecard
One ship-readiness scorecard rolling up tool definitions, server.json, OAuth, transport, tool poisoning, and spec compliance into a graded gap report.
Open tool →Agent Spend-Control Feature Matrix
Compare agent connections, user delegation, AP2 mandates, x402, Visa VIC token scope, and Mastercard agentic tokens on identity model, budget granularity, attenuation, expiry, revocation, and audit attribution. Every cell cites a dated source.
Open tool →PayPal Dispute Deadline & Evidence
PayPal dispute seller-response deadlines and the evidence bundle a seller needs: snapshot-stated inquiry windows and seller_response_due_date passthrough, mapped to reason-to-evidence packs.
Open node →Agent Spend-Policy Simulator
Simulate thousands of synthetic AP2 agent transactions against a user-authored spend policy and surface scope creep, limit violations, and expiry drift.
Open node →x402 / Crypto-Rail Settlement Cost & Finality Modeler
Model settlement cost and finality time for agent payments across x402, Stripe USDC on Base, card rails, and bank transfer, with a rail-selection recommendation.
Open node →Agent Identity & Authorization Attestation Checker
Validate AI agent identity credentials and delegated-authority chains against the KYA-OS (Know Your Agent OS) specification from the DIF Trusted AI Agents WG.
Open node →ACP Checkout Conformance Validator
Validate ACP CheckoutRequest and CheckoutResponse payloads against the OpenAI and Stripe specification, including Shared Payment Token scope rules.
Open node →Signature Agent Card Validator
Validate the Signature Agent Card (Cloudflare and Bedrock AgentCore schema): required fields present and card keys consistent with the validated directory.
Open node →Agent Key Rotation Auditor
Audit agent key freshness and rotation posture: key age against max-age policy, presence of a next key, and Ed25519 algorithms.
Open node →Agent Payment Rail Trust Crosswalk
Crosswalk agent identity posture to Visa TAP, Mastercard Agent Pay, and Web Bot Auth acceptance criteria, with a per-rail verdict.
Open node →Agent Directory Publish Readiness Diagnostic
Diagnose readiness to publish a verifiable Web Bot Auth identity: well-known path, JWKS reachability, card completeness, and rotation.
Open node →Agent On-Behalf-Of Mandate Validator
Validate an on-behalf-of mandate: subject, intent, scope list, and expiry, as the middle node of the agent-authorization-lifecycle workflow.
Open node →Where to read next
The neighboring pages that carry the rest of the story: the protocols behind agentic checkout, the evidence side of disputes, and how agent activity is observed once money moves.
Authored 2026-10-25 · Post Oak Labs