kazulog@sv2:~$ sudo cloud-init schema --config-file /tmp/good.yaml
Valid schema /tmp/good.yaml
kazulog@sv2:~$ sudo cloud-init schema --config-file /tmp/bad.yaml
Invalid user-data /tmp/bad.yaml
Error: Cloud config schema errors: packages: 'git' is not of type 'array', runcmds: Additional properties are not allowed ('runcmds' was unexpected)

Error: Invalid schema: user-data

kazulog@sv2:~$ sudo cloud-init schema --system | tail -3
2. network-config at /var/lib/cloud/instances/ubuntu/network-config.json:
  Valid schema network-config