write.cs

using LEGO.AsyncAPI;
using LEGO.AsyncAPI.Models;

// Build the document 
var document = new AsyncApiDocument()
{
    Info = new AsyncApiInfo
    {
        Title = "Example",
        Version = "0.1.0"
    }
};

// Add the channel
document.Channels["user/signedup"] = new AsyncApiChannel()
{
    Subscribe = new AsyncApiOperation()
    {
        Message = new List<AsyncApiMessage>()
        {
            new AsyncApiMessage()
            {
                Description = "An event describing that a user just signed up.",
                // The payload consists of one or more layers of JsonSchema why it can look a bit daunting
                Payload = new AsyncApiSchema()
                {
                    Type = new List<SchemaType>()
                    {
                        SchemaType.Object,
                    },
                    Properties = new Dictionary<string, AsyncApiSchema>()
                    {
                        {
                            "fullName", new AsyncApiSchema()
                            {
                                Type = new List<SchemaType>()
                                {
                                    SchemaType.String,
                                }
                            }
                        },
                        {
                            "email", new AsyncApiSchema()
                            {
                                Type = new List<SchemaType>()
                                {
                                    SchemaType.String
                                },
                                Format = "email",
                            }
                        },
                        {
                            "age", new AsyncApiSchema()
                            {
                                Type = new List<SchemaType>()
                                {
                                    SchemaType.Integer,
                                },
                                Minimum = 18,
                            }
                        }
                    }
                }
            }
        }
    }
};

// Serialize the document to yaml
var serialized = document.Serialize(AsyncApiVersion.AsyncApi2_0, AsyncApiFormat.Yaml);
Console.WriteLine(serialized);