[signaler]

A very simple example is that of Google which gives you a Wikipedia summary of a topic, but that's too simple.

In your case you are looking for some way to heatmap certain keywords, or even the tone of a piece of content. You could go further and see the context of the content (which is presumably some form of document which can be parsed).

There are innumerable things online to do this. My first port of call is to trawl Github and find a repo on there which does this.

Just be careful of online services which are hoovering up your query and making off with your data...