The correct option is action.yml.

GitHub Actions reads action.yml at the root of the action directory to define the action metadata. This file declares the name and description along with inputs and outputs and the runtime configuration. It tells GitHub whether the action is JavaScript, a Docker container, or a composite action and it provides the entry point and how inputs map to arguments and outputs.

workflow.yaml is used for workflow files in .github/workflows and it defines repository automation rather than metadata for a reusable action.

requirements.yaml is not a GitHub Actions metadata file and it belongs to other ecosystems and it does not define action inputs, outputs, or runtime behavior.

action.json is not valid for action metadata since GitHub requires a YAML metadata file and JSON is not supported for this purpose.

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