It is a simple command line tool that can be installed from NuGet. When run, it will take a C# database migration context assembly, and create an entity relationship (ER) diagram in Mermaid syntax.

You can install the siren-gen tool via the following .NET command

dotnet tool install -g Gman.Siren

The tool takes two arguments with an optional third:

siren-gen <PATH_TO_MIGRATION_ASSEMBLY> <PATH_TO_OUTPUT_MARKDOWN_FILE> <MARKDOWN_ANCHOR>

• PATH_TO_MIGRATION_ASSEMBLY - this will be the location of the built .NET DLL containing the database migration you wish to map to an ER diagram.
• PATH_TO_OUTPUT_MARKDOWN_FILE - this points to a file (on your local file system) where the markdown should be generated; includes the full file name. The file does not have to be a markdown (.md) file.
• MARKDOWN_ANCHOR - this is useful for updating README.md files that may be associated with your domain model (i.e. committed in a git repository). If the markdown anchor is specified, and the output file contains that markdown anchor (for example "### My Domain Model Diagram"), then the Siren tool will only add or replace any existing diagram it finds under that anchor, and leave the rest of the document unmodified.

Take the following classes

public class Customer
{
	[Key]
	public Guid CustomerId { get; set; }

	public string FirstName { get; set; }

	public string MiddleName { get; set; }

	public string LastName { get; set; }
}

public class Order
{
	[Key]
	public Guid OrderId { get; set; }

	[ForeignKey("CustomerReference")]
	public Guid CustomerId { get; set; }

	public virtual Customer CustomerReference { get; set; }

	public long ReferenceNumber { get; set; }

	public DateTime DatePlaced { get; set; }
}

When running the tool, the output file should produce the following:

	erDiagram
	Customer {
		Guid CustomerId PK
		String FirstName 
		String MiddleName 
		String LastName 
	}
	Order {
		Guid OrderId PK
		Guid CustomerId FK
		Int64 ReferenceNumber 
		DateTime DatePlaced 
	}
Customer||--|{Order : ""