Indexes in Entity Framework Data Annotations

[Index(nameof(Url))]
public class Blog
{
    public int BlogId { get; set; }
    public string Url { get; set; }
}

Composite index

[Index(nameof(FirstName), nameof(LastName))]
public class Person
{
    public int PersonId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

Index uniqueness

[Index(nameof(Url), IsUnique = true)]
public class Blog
{
    public int BlogId { get; set; }
    public string Url { get; set; }
}

Index sort order

[Index(nameof(Url), nameof(Rating), AllDescending = true)]
public class Blog
{
    public int BlogId { get; set; }
    public string Url { get; set; }
    public int Rating { get; set; }
}

[Index(nameof(Url), nameof(Rating), IsDescending = new[] { false, true })]
public class Blog
{
    public int BlogId { get; set; }
    public string Url { get; set; }
    public int Rating { get; set; }
}

Index name

[Index(nameof(Url), Name = "Index_Url")]
public class Blog
{
    public int BlogId { get; set; }
    public string Url { get; set; }
}

References
https://learn.microsoft.com/en-us/ef/core/modeling/indexes?tabs=data-annotations