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Version: v3.9.x

The gator CLI

Feature State: Gatekeeper version v3.7+ (alpha)

The gator CLI is a tool for evaluating Gatekeeper ConstraintTemplates and Constraints in a local environment.


To install gator, you may either download the binary relevant to your system or build it directly from source. On macOS and Linux, you can also install gator using Homebrew.

To build from source:

go get

Install with Homebrew:

brew install gator

The gator test subcommand

gator test allows users to test a set of Kubernetes objects against a set of Templates and Constraints. The command returns violations when found and communicates success or failure via its exit status.

Note: The gator verify command was first called gator test. These names were changed to better align gator with other projects in the open-policy-agent space.


Specifying inputs

gator test supports inputs through the --filename flag and via stdin. The two methods of input can be in combination or individually.

The --filename flag can specify a single file or a directory. If a file is specified, that file must end in one of the following extensions: .json, .yaml, .yml. Directories will be walked, and any files of extensions other than the aforementioned three will be skipped.

For example, to verify a manifest (piped via stdin) against a folder of policies:

cat my-manifest.yaml | gator test --filename=template-and-constraints/

Or you can specify both as flags:

gator test -f=my-manifest.yaml -f=templates-and-constraints/

Exit Codes

gator test will return a 0 exit status when the objects, Templates, and Constraints are successfully ingested, no errors occur during evaluation, and no violations are found.

An error during evaluation, for example a failure to read a file, will result in a 1 exit status with an error message printed to stderr.

Policy violations will generate a 1 exit status as well, but violation information will be printed to stdout.

Enforcement Actions

While violation data will always be returned when an object is found to be violating a Constraint, the exit status can vary. A constraint with spec.enforcementAction: "" or spec.enforcementAction: deny will produce a 1 exit code, but other enforcement actions like dryrun will not. This is meant to make the exit code of 1 consistent with rejection of the object by Gatekeeper's webhook. A Constraint set to warn would not trigger a rejection in the webhook, but would produce a violation message. The same is true for that constraint when used in gator test.

Output Formatting

gator test supports a --output flag that allows the user to specify a structured data format for the violation data. This information is printed to stdout.

The allowed values are yaml and json, specified like:

gator test --filename=manifests-and-policies/ --output=json

The gator verify subcommand

Writing Test Suites

gator verify organizes tests into three levels: Suites, Tests, and Cases:

  • A Suite is a file which defines Tests.
  • A Test declares a ConstraintTemplate, a Constraint, and Cases to test the Constraint.
  • A Case defines an object to validate and whether the object is expected to pass validation.

Any file paths declared in a Suite are assumed to be relative to the Suite itself. Absolute paths are not allowed. Thus, it is possible to move around a directory containing a Suite, and the files it uses for tests.


An example Suite file.

To be valid, a Suite file must declare:

kind: Suite

gator verify silently ignores files which do not declare these. A Suite may declare multiple Tests, each containing different Templates and Constraints. Each Test in a Suite is independent.


Each Suite contains a list of Tests under the tests field.

A Test compiles a ConstraintTemplate, and instantiates a Constraint for the ConstraintTemplate. It is an error for the Constraint to have a different type than that defined in the ConstraintTemplate spec.crd.spec.names.kind, or for the ConstraintTemplate to not compile.


Each Test contains a list of Cases under the cases field.

A Case validates an object against a Constraint. The case may specify that the object is expected to pass or fail validation, and may make assertions about the returned violations (if any).

A Case must specify assertions and whether it expects violations. The simplest way to declare this is:

The Case expects at least one violation:

- violations: yes

The Case expects no violations:

- violations: no

Assertions contain the following fields, acting as conditions for each assertion to check.

  • violations is either "yes", "no", or a non-negative integer.
    • If "yes", at least one violation must otherwise match the assertion.
    • If "no", then no violation messages must otherwise match the assertion.
    • If a nonnegative integer, then exactly that many violations must match. Defaults to "yes".
  • message matches violations containing the exact string specified. message is case-sensitive. If not specified or explicitly set to empty string, all messages returned by the Constraint are considered matching.

A Case may specify multiple assertions. For example:

  - name: both-disallowed
object: samples/repo-must-be-openpolicyagent/disallowed_both.yaml
- violations: 2
- message: initContainer
violations: 1
- message: container
violations: 1

This Case specifies:

  • There are exactly two violations.
  • There is exactly one violation containing "initContainer".
  • There is exactly one violation containing "container".

It is valid to assert that no violations match a specified message. For example, the below is valid:

- violations: yes
- violations: no
message: foobar

This Case specifies that there is at least one violation, and no violations contain the string "foobar".

A Case may specify inventory, which is a list of paths to files containing Kubernetes objects to put in data.inventory for testing referential constraints.

- samples/data_objects.yaml

More examples of working gator verify suites are available in the gatekeeper-library repository.


To run a specific suite:

gator verify suite.yaml

To run all suites in the current directory and all child directories recursively

gator verify ./...

To only run tests whose full names contain a match for a regular expression, use the run flag:

gator verify path/to/suites/... --run "disallowed"

Run gator verify --help for more information.


Duplicate violation messages

Rego de-duplicates identical violation messages. If you want to be sure that a test returns multiple violations, use a unique message for each violation. Otherwise, if you specify an exact number of violations, the test may fail.

Matching is case-sensitive

Message declarations are case-sensitive. If a test fails, check that the expected message's capitalization exactly matches the one in the template.

Referential constraints and Namespace-scoped resources

Gator cannot determine if a type is Namespace-scoped or not, so it does not assign objects to the default Namespace automatically. Always specify metadata.namespace for Namespace-scoped objects to prevent test failures, or to keep from specifying templates which will fail in a real cluster.

Platform Compatibility

gator is only automatically tested on Linux for each commit. If you want to use gator on other systems, let us know by replying to this issue.

gator verify has been manually tested on Windows and works as of this commit. Continued functionality is not guaranteed.

File paths which include backslashes are not portable, so suites using such paths will not work as intended on Windows.