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)