Configuration as Code
Treating CI configuration like any other source code makes it easy to manage and share. All environment variables you store inside CircleCI are encrypted at rest and sent to your build containers using SSH.
Increase Developer Productivity
Jenkins often requires a team of engineers on-call to install dependencies and troubleshoot issues. With CircleCI, this isn’t necessary. All builds start in a clean environment and can be debugged by any developer using SSH into builds.
Reduce Operational Overhead
Plugins are required to do almost anything in Jenkins; even checking out a Git repo. CircleCI saves you the trouble of managing and installing plugins because all core CI functionality is built in, including first-class integrations with GitHub and BitBucket.
Developer at Avvo
“With CircleCI, we have probably saved $75-300K in maintenance on Jenkins. We've also had fewer headaches and shipping is easy.”