AlchemyAPI provides easy-to-use mechanisms to identify positive/negative sentiment within any document or web page.
AlchemyAPI Sentiment Analysis APIs are capable of computing document-level sentiment, user-specified sentiment targeting, entity-level sentiment, and keyword-level sentiment. Multiple modes of sentiment analysis provide for a variety of use cases ranging from social media monitoring to trend analysis.

API endpoints are provided for performing sentiment analysis on Internet-accessible URLs and posted HTML files.
Extracted meta-data may be returned in XML, JSON, and RDF formats. More information on Sentiment Analysis API response formats is available.