PriceWin plugin for Hermes

Live hotel and flight prices compared across Booking.com, Agoda, Trip.com and Traveloka, in one install. A portable Agent Plugins v1 package that bundles:

mcp.json — the PriceWin MCP server, https://mcp.price.win/mcp (Streamable HTTP, no account, no API key);
skills/pricewin-travel-search — how to run a search (results arrive in two steps), ask for what the guest has not said, and read prices in USD;
desktop/plugin.js — inline hotel and flight cards in the Hermes Desktop transcript instead of raw text.

Install

hermes plugins install pricewin
hermes plugins enable pricewin

Start a new session so the MCP tools load. The tools appear as mcp_pricewin_<tool>.

The server exposes all twelve of its tools, including the four that act on a booking: request_booking sends a request the hotel confirms (nothing is charged, no room is held, the guest pays at the property), check_booking_status reads it back, and cancelling takes a single-use token emailed to the guest (request_cancel_token, then cancel_booking), so nothing is cancelled without the guest's own inbox.

What it renders

The agent writes a directive on its own paragraph and the transcript replaces it with a card:

::pricewin-hotel{name="Liberty Central Riverside" price="58" stars="4"
                 area="District 1, Ho Chi Minh City" ota="agoda"
                 link="agoda.com/liberty-central/hotel/ho-chi-minh-city-vn.html?..."}

::pricewin-flight{route="SGN → HAN" airline="Vietnam Airlines" price="72"
                  depart="06:15" duration="2h10m" stops="0"
                  link="trip.com/flights/..."}

link has no https:// and no www.. Hermes Desktop turns any URL in a message into a hyperlink before it looks for directives, and a directive with a hyperlink inside is no longer one — it shows as raw text. The PriceWin MCP server gives every result a ready-made link in this form, trimmed to the dates and party so it fits the 1024-character attribute limit. A directive that uses url="https://…" instead is still read when it survives.

The desktop half is off by default after install: turn it on under Capabilities → Plugins → PriceWin → Desktop.

Directive	Attributes
`pricewin-hotel`	`name` (required), `price` (USD), `stars` (1–5), `area`, `ota`, `note`, `link`
`pricewin-flight`	`route` (required), `price` (USD), `airline`, `depart`, `duration`, `stops`, `link`

The pricewin-travel-search skill is what teaches the agent to emit these.

Safety

Directive attributes are untrusted model output, so the plugin validates all of them and drops anything it cannot parse:

The link (link, or the older url) must resolve to https: and be on PriceWin or one of the OTAs the search results link to (Agoda, Booking.com, Traveloka, Trip.com), subdomains included. Any other host renders no link at all, so a hallucinated URL never becomes a click target. The button label names the site from the URL itself, never from the model's text.
price must be a positive number; stars must be 1–5.
A card with no name (hotel) or route (flight) renders nothing.

The Desktop half makes no network requests, reads no files, and stores no state. Links open in the system browser through ctx.os.openExternal. A card never takes a booking or a payment: an OTA result is booked on the linked site, and no step anywhere in this plugin takes money.

Development

desktop/plugin.js is loaded uncompiled — there is no build step, and JSX syntax will not parse. UI is written with jsx() / jsxs() calls, and @hermes/plugin-sdk, react and react/jsx-runtime are the only importable specifiers, which is why the plugin is a single file.

To develop against a live app, symlink the package into the Hermes home and reload desktop plugins (⌘K → Reload desktop plugins):

ln -s "$PWD" ~/.hermes/plugins/pricewin
hermes plugins doctor pricewin
hermes plugins validate pricewin

License

MIT

pricewin

Screenshots

README