As I’m using more and more often Jenkins Pipelines, I found the need to validate a Jenkinsfile in order to fix syntax errors before committing the file into version control and running the pipeline job in Jenkins. This can saves some time during development and allows to follow best practices when writing a Jenkinsfile as validation returns both errors and warnings.

There are several ways to validate a Jenkinsfile and some editors like VS Code even have a built-in linter. Personally, the easiest way I found is to validate a Jenkinsfile is to run the following command from the command line (provided you have Jenkins running somewhere):

curl --user username:password -X POST -F "jenkinsfile=<Jenkinsfile" http://jenkins-url:8080/pipeline-model-converter/validate

Note the following:

1. If your Jenkins is authenticating users, you need to pass the username and password otherwise you can omit that part.
2. By default, this command expects your Jenkinsfile to be called Jenkinsfile. If not, change the name in the command.
3. Replace jenkins_url and possibly port 8080 based on the URL and port where you are running Jenkins. You can also use localhost as URL if you are running Jenkins on your machine.

If the Jenkinsfile validates, it will show a message like this one:

Jenkinsfile successfully validated.

Or, if you forgot to use steps within stage in your Jenkinsfile, the validation will flag an error like this:

Errors encountered validating Jenkinsfile:
WorkflowScript: 10: Unknown stage section "git". Starting with version 0.5, steps in a stage must be in a ‘steps’ block. @ line 10, column 9.
           stage('Checkout Code') {
           ^

WorkflowScript: 10: Expected one of "steps", "stages", or "parallel" for stage "Checkout Code" @ line 10, column 9.
           stage('Checkout Code') {
           ^

Happy validation!