This documentation was written because there doesn't seem to be a five-minute introduction anywhere on their site. I had to hit multiple web sites to compile this basic information.
Your log4j.xml must contain an appender that goes to a file and uses the XMLLayout. Here's a sample:
<appender name="chainsaw_log" class="org.apache.log4j.RollingFileAppender">
<param name="File" value="blipfoot.log.xml"/>
<param name="Append" value="true"/>
<param name="Threshold" value="DEBUG"/>
<param name="MaxFileSize" value="100MB"/>
<param name="MaxBackupIndex" value="2"/>
<layout class="org.apache.log4j.xml.XMLLayout" />
You can use Chainsaw 1.2, which ships inside the log4j distribution. Run it like this:
java -classpath log4j-1.2.12.jar org.apache.log4j.chainsaw.Main
Or you can use Chainsaw 2, which is at this Java Web Start link.
Version 2 gives you pretty colors, I haven't yet figured out how to filter by logging level, which is pretty important. Version 1.2 couldn't make it any clearer: there's a level drop down placed prominently.