What it does
The RSS to JSON API turns a feed into JSON your code can read. Send a feed URL, or upload the XML. You get the feed's items back as structured JSON, ready to store, filter or render.
Use the /url endpoint to fetch and parse a remote feed in one step. That is the usual case: polling a blog, a news site or a podcast feed on a schedule. Use the /file endpoint when you already hold the XML, such as an archived feed or one a partner sent you. Set detailed=true when you need [what detailed adds] instead of the summary fields.
It handles both of the feed formats in use on the web today. RSS is the common one. Atom is the format WordPress, Blogger and YouTube publish, and a parser built only for RSS will choke on it. Either one works here, with the same call.
Why call an API instead of installing a feed parser? Because feeds in the wild are inconsistent. Missing dates. Odd encodings. Namespaced extensions. Formats that differ from one publisher to the next. Those edge cases show up one at a time in production, and then they are yours to fix. Here they stay on this side of the call.
Most feeds update a few times a day at most. Cache the result and poll on a sensible interval rather than parsing on every page load.
Working with XML more generally? Use Convert XML to JSON for arbitrary XML documents, or Convert JSON to XML for the reverse.