Wheelwise
UK used-car listings with fair-price grade, 36-month resale forecast and monthly cost per advert

US vehicle recalls, complaints, fuel economy, crash ratings, service bulletins and VIN decoding.
WhichTrim API is a free Vehicle API that requires apiKey authentication, is served over HTTPS and supports CORS, so it can be called from the browser.
REST API documentation for WhichTrim: vehicles, recalls, advisories, grades, trims and specs for every U.S.
Details from whichtrim.com.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
UK used-car listings with fair-price grade, 36-month resale forecast and monthly cost per advert
Lock and unlock vehicles and get data like odometer reading and location. Works on most new cars
Owner complaints, recalls and failure-mileage statistics by vehicle make, model and year
NHTSA safety recalls by model year, make and model with component, consequence and remedy
The WhichTrim API is provided by WhichTrim (whichtrim.com). REST API documentation for WhichTrim: vehicles, recalls, advisories, grades, trims and specs for every U.S.
Yes. The WhichTrim API is listed in the Vehicle category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The WhichTrim API uses apiKey authentication, so you need to register for credentials before making requests.
Yes. The WhichTrim API supports CORS, so front-end JavaScript can call it directly.
Yes. The WhichTrim API is served over HTTPS, so it's safe to use in production.