YEdit is a YAML editor for Eclipse. See the wiki for more details

Use the Eclipse Marketplace client.

or

Use the Eclipse update site found here: http://dadacoalition.org/yedit

or

Download the .jar file from releases page and place it in the plugins directory of you Eclipse installation.

YEdit is licensed under the Eclipse Public License (https://www.eclipse.org/legal/epl-v10.html)