Surfer uses the NLP API of Google to extract the data about entities and sentiment. To deepen our analysis and make the data actionable, we cross it with our True Density calculations.
In terms of Sentiment, we use similar procedures to IBM Watson and measure the overall sentiment of page content.
If you're interested in finding out more about our decision to use IBM Watson for page sentiment, Slawek explains it in our article on NLP and on-page SEO.
We also label the sentiment of each NLP entity for you as part of true density section of your Audit.
NLP entities have been incorporated into the SERP Audit. You’ll find them in the True Density section where relevant phrases and words that have been labeled by Google as NLP entities are marked with the NLP icon
We have also factored in NLP when creating new content too. The Content Editor highlights NLP entities when you set up / customize the content draft. They are identified with a blue sash.
TIP: NLP Entities help understand Google your content better. Use them in your content!