Introduction

Validating YAML values to be of specific data types is a common need for many situations. Ensuring that the values in your YAML file are valid is essential to avoid configuration-related errors. This How-to Guide checks and ensures each value in a YAML file is the data type it’s supposed to be, using the CUE command line.

Prerequisites

• You have CUE installed locally. This allows you to run cue commands

Requirements

• Using the command line or terminal
• File editing

Steps

Create a YAML file called x.yaml with the following:

people:
  Gopher:
    name: Gopher
    age: 12
    address: Mountain View
  Ken:
    name: Ken
    age: 21
    address: The Blue Sky

Create a CUE file named x.cue

The following CUE creates a CUE definition that describes the data type constraints for every person.

#Person: {
	name:    string
	age:     int
	address: string
}

people: [X=string]: #Person & {
	name: X
}

Run the following cue command in your:

$ cue vet -c x.cue x.yaml

NOTE: cue vet is silent when run successfully. Output will only show on error.

Add another person to your YAML data.

people:
  Gopher:
    name: Gopher
    age: 12
    address: Mountain View
  Ken:
    name: Ken
    age: 21
    address: The Blue Sky
  Rob:
    name: Rob
    age: 42.2
    address: CUEtopia

Validate again with cue vet

$ cue vet -c x.cue x.yaml
people.Rob.age: conflicting values 42.2 and int (mismatched types float and int):
    ./x.cue:3:11
    ./x.yaml:12:10

The command output shows validation errors where the YAML violates the (type) constraints that you have declared.

Fix up the YAML

people:
  Gopher:
    name: Gopher
    age: 12
    address: Mountain View
  Ken:
    name: Ken
    age: 21
    address: The Blue Sky
  Rob:
    name: Rob
    age: 42
    address: CUEtopia

Validate with cue vet again

$ cue vet -c x.cue x.yaml

The cue vet command will show no output on success.

Well done! Any future data errors on names, ages, and addresses in your YAML will be detected. This is especially helpful with YAML files with 100s (and even 1000s) of lines.

Further reading/See Also

• cmd/cue command line documentation