faregrid
faregrid is a small local bridge to the hosted
FlightPowers MCP server, which reads live flight prices
from Google Flights. Give it an origin and a destination,
plus either a single date or a whole date range, and it
answers with fares, airlines, durations, stop counts, a
bookable link for each flight, and the historical price
band that shows whether a fare is unusually cheap or
expensive for that route.
The bridge keeps no fare data of its own. It serves the
upstream server's tool list locally, exactly as captured
from the live endpoint, and forwards each tool call
upstream, returning the result untouched. The captured
surface is search only: results carry a buy_link to
book on the vendor's own flow, and there is no booking,
purchase, or payment tool in it.
Tools
search_oneway_flights — one-way fares. Required:
from_airport and to_airport (IATA codes; the
destination may be several codes as "BCN,LIS,ATH" or
["BCN","LIS","ATH"]). Optional: departure_date, or
a range via departure_date_from / departure_date_to,
max_stops, airline_codes, exclude_airline_codes,
departure and arrival hour windows, currency
(default "usd"), max_price, seat_type,
passengers, sort_by (default "best"), limit
(default 10), max_searches, use_fallback, and
verbose. One call can search every date/destination
combination in a range.search_roundtrip_flights — round-trip fares, priced
as paired legs rather than two separate one-ways.
Required: from_airport and to_airport. Optional:
the same departure date or range fields as the one-way
tool, plus return_date or nights (a trip length, or
a list like [5, 6, 7]), max_departure_stops,
max_return_stops, departure_airline_codes,
return_airline_codes, returns_per_outbound, and
the shared currency, max_price, seat_type,
passengers, sort_by, limit, max_searches,
use_fallback, and verbose fields.
Fares go stale within minutes, so a current price always
comes from a new search rather than an earlier result.
Configuration
FLIGHTPOWERS_MCP_URL (optional) — override the
upstream endpoint. Defaults to
https://flights.flightpowers.com/mcp. (The override
hook is this rebuild's own labelled reconstruction.)FLIGHTPOWERS_API_KEY (optional) — when set, every
upstream request carries an
x-rapidapi-key: <key> header, for the caller's own
RapidAPI key for the Google Flights Live API. When it
is not set, no key header is sent and the upstream
applies its free sign-in allowance. No Authorization
header is ever sent. (This forwarding is also a
labelled reconstruction; the original surface was
captured keyless.)
Forwarding mechanics
On the first tool call the client opens a streamable
HTTP session with the upstream: a JSON-RPC initialize
request (protocolVersion 2025-03-26, clientInfo name
faregrid), then a notifications/initialized
notification, then the tools/call request carrying
the caller's arguments unchanged. When the upstream
answers initialize with an Mcp-Session-Id header,
that value rides on every later request of the session,
which is reused for the life of the process. Replies
may arrive as plain JSON or as server-sent events;
both are read.
Successful upstream results pass through verbatim,
including any isError flag the upstream sets.
Failures — a JSON-RPC error, a non-2xx status, an
unreadable response, or a request that cannot be
completed — come back as an isError result whose
text starts with faregrid error: (this rendering
is this rebuild's own labelled reconstruction).
CLI
Each tool is also a subcommand taking one JSON argument
string:
Exit codes: 0 on success, 1 on an isError
result, 2 on a usage error.
MCP server
MCP client config:
Docker
The container's default command is mcp, so the first
form is a stdio MCP server; any other arguments reach
the CLI normally.
Development
The test suite runs entirely against a stubbed
JSON-RPC upstream — no live network calls.
License
MIT — see LICENSE.
