> For the complete documentation index, see [llms.txt](https://docs.snyk.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.snyk.io/scan-fix-and-prevent/scan-with-snyk/snyk-iac/current-iac-custom-rules/writing-rules-using-the-sdk/custom-rego-builtins.md).

# Custom Rego Builtins

The custom Rego built-in functions available for Snyk IaC custom rules

The SDK also registers some helper Rego functions that can be used while testing.

These are:

* `hcl2.unmarshal_file`: takes in the path to a file and parses it from HCL2 format to JSON
* `yaml.unmarshal_file`: takes in the path to a file and parses it from YAML format to JSON

These functions are used by the testing framework at `lib/testing/main.rego` so that you can pass in the path to fixture files instead of having to generate the JSON fixture yourself.


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