The dependabot.yml configuration file requires a minimum set of fields for each package manager entry defined under the updates key. According to the official GitHub documentation, three fields are mandatory to define a basic update check:

1. package-ecosystem: Specifies the package manager to use (e.g., npm, maven, pip).

2. directory: Defines the location of the package manifest files (e.g., / for the root directory).

3. schedule.interval: Sets the frequency for checking for new versions (e.g., daily, weekly).

Without these three fields, Dependabot cannot identify which dependencies to monitor, where to find them, or how often to check for updates.

C. milestone: This is an optional field used to automatically assign a specific milestone to all pull requests created by Dependabot for that configuration.

E. allow: This is an optional field used to explicitly specify which dependencies Dependabot should update, which is useful for limiting updates to a specific subset.

1. GitHub Docs, "Configuration options for the dependabot.yml file." This official documentation provides a comprehensive list of all available configuration options and explicitly labels which are required and which are optional.

Section: "Required properties for each package manager": This section explicitly lists package-ecosystem, directory, and schedule (which contains the required interval field) as mandatory for each entry in the updates array.

Section: "Optional properties for all updates": This section lists milestone and allow as optional configurations that provide more granular control over Dependabot's behavior.