The fueleconomy.gov API is public and requires no API key; start by fetching available model years via GET https://www.fueleconomy.gov/ws/rest/vehicle/menu/year
Use the chained menu endpoints to get makes for a year and models for a make: GET /ws/rest/vehicle/menu/make?year=<year> then /ws/rest/vehicle/menu/model?year=<year>&make=<make>
Retrieve the list of vehicle options (trim/engine combinations) via GET /ws/rest/vehicle/menu/options?year=<year>&make=<make>&model=<model> to obtain vehicle IDs
Fetch full fuel economy details for a specific vehicle ID: GET /ws/rest/vehicle/<id> which returns city, highway, and combined MPG along with CO2 emissions and fuel type
For EVs and PHEVs, look for the mpgE (MPG equivalent) and range fields in the response; the combined field for EVs reflects MPGe, not liquid fuel economy
Known gotchas
The API returns XML by default; append format=json is not universally supported across all endpoints — use an Accept: application/json header or parse XML responses
Vehicle IDs are specific to EPA trim/configuration records and do not correspond to VINs or any other industry identifier; you must traverse the menu hierarchy each time to resolve an ID
Fuel economy data for the current model year may be incomplete early in the calendar year as not all vehicles have been tested yet; always check that the returned values are non-null before displaying
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