Which web feed format was first released by Netscape in 1999? The answer is RSS.
Netscape released RSS 0.90 in March 1999 for its My Netscape portal. The name originally meant RDF Site Summary, and the format let websites publish structured updates that portals and later feed readers could retrieve automatically.
RSS was not a single, continuously controlled standard. Netscape released RSS 0.91 later in 1999, while subsequent versions developed along separate branches. RSS 1.0 came from the RSS-DEV Working Group, and RSS 2.0 was advanced by UserLand and later maintained through Harvard.
A common mix-up is Atom, another web-feed format created later in response to disagreements over RSS's direction. OPML is mainly an outline and subscription-list format, while JSON Feed is a much newer JSON-based alternative rather than Netscape's 1999 format.