testbed/aws-cloudformation__cfn-lint/docs/format_keyword.md

The format keyword

The format keyword in JSON Schema is used to define a regular expression pattern that a string value should match. It provides a way to validate that a string adheres to a specific format or pattern.

In cfn-lint, we have extended the format keyword to support custom formats that are specific to AWS resources. These custom formats help validate values against specific patterns or constraints defined by AWS.

Custom Formats

cfn-lint supports the following custom formats:

AWS::EC2::VPC.Id

This format ensures that the value is a valid VPC ID, which is a string of the pattern vpc-[0-9a-f]{8} or vpc-[0-9a-f]{17}.

AWS::EC2::SecurityGroup.GroupId

This format validates that the value is a valid Security Group ID, which is a string of the pattern sg-[0-9a-f]{8} or sg-[0-9a-f]{17}.

AWS::EC2::SecurityGroup.GroupName

This format validates that the value is a valid Security Group Name, which must be a string of 1 to 255 characters, starting with a letter, and containing only letters, numbers, and certain special characters.

AWS::EC2::Image.Id

This format validates that the value is a valid Amazon Machine Image (AMI), which is a string of the pattern ami-[0-9a-f]{8} or ami-[0-9a-f]{17}. More info in docs