In production

Siz — AI Commerce Gateway (MCP)

AI assistants that book your tickets, then hand payment back to you.

MCP
Go
OAuth 2.1

Screenshot of a Claude chat where the assistant books tickets through the Siz MCP server — Claude booking tickets through Siz

Client: F&B and AI-commerce company
Timeline: Aug 2026 – Present
Role: Backend & AI Engineer
Outcome: Live MVP

About the project

An MCP server that lets AI assistants search and book cinema and flight tickets on real merchant sites, then hands payment back to the user's own banking app. Accounts link with OAuth 2.1 + PKCE, every merchant call is signed (Ed25519, RFC 9421) and VietQR codes are verified before a user sees them; an AI-Ready scorer grades how well agents can use a merchant site. Two-person product team since Aug 2026: I built the gateway and its web app.

The problem

Vietnamese merchants have no API an AI assistant can use. A user can ask Claude or ChatGPT to find a cinema seat or a flight, but the assistant cannot actually book it on the user's behalf, and nobody wants an AI holding their money. Siz exists to close that gap safely.

What I built

Siz is an AI commerce gateway built as an MCP (Model Context Protocol) server. I work in a two-person product team, since August 2026, and I built the gateway and its web app:

Booking tools for assistants — MCP tools that let an AI assistant search and book cinema and flight tickets on real merchant sites.
Account linking — users connect their assistant to Siz with OAuth 2.1 + PKCE, and can review and revoke connected assistants from a "manage connections" page.
Signed merchant requests — every request Siz sends to a merchant is signed with Ed25519 following RFC 9421 (HTTP Message Signatures), so the merchant can verify it really came from Siz.
Payment handed back — Siz never holds money. It returns a VietQR code that is verified before the user sees it, and the user pays in their own banking app.
AI-Ready scorer — a crawler that grades merchant sites on how usable they are for AI agents, plus a merchant integration guide.

How it works

An assistant calls Siz's MCP tools with the user's linked account. Siz turns the request into calls against the merchant's site, signs each one, and walks the booking up to the point of payment. At that point control returns to the human: the assistant shows a verified VietQR and the user approves the payment in their bank app. The agent can do the tedious part; the money decision stays with the person.

Outcome

Siz is a live MVP: an assistant can book tickets through it end to end, with account linking, signed merchant calls and verified payment hand-off in place. The web app covers consent, connection management, the AI-Ready score report and the merchant guide.