Looking for API where books can look up. I want to pass a keyword and get back list of book titles and thumbnails. Like Rotten Tomatoes for movies. I want to use it for book recommendation.
Goodreads has an API that allows you to fetch all sorts of information about books. You can access them when you register for a developer key. Below is the one that matches your question:
Get the reviews for a book given a title string
Get an xml response that contains embed code for the iframe reviews widget, which shows an excerpt (first 300 characters) of the most popular reviews of a book for a given title/author. The book shown will be the most popular book that matches all the keywords in the input string. The reviews are from all known editions of the book.
URL: https://www.goodreads.com/book/title.FORMAT (sample url)
HTTP method: GET
format: xml or json
key: Developer key (required).
title: The title of the book to lookup.
author: The author name of the book to lookup. This is optional, but is recommended for accuracy.
rating: Show only reviews with a particular rating (optional)