The .NET DUID

Michael Argentini/Tuesday, December 9, 2025

DUID is a fully-featured replacement for GUIDs (Globally Unique Identifiers). They are more compact, web-friendly, and provide more entropy than GUIDs. We created this UUID type as a replacement for GUIDs in our projects, improving on several GUID shortcomings.

We pronounce it doo-id, but it can also be pronounced like dude, which is by design :)

You can use DUIDs as IDs for user accounts and database records, in JWTs, as unique code entity (e.g. variable) names, and more. They're an ideal replacement for GUIDs that need to be used in web scenarios.

Key security features:

Uses the latest .NET cryptographic random number generator
More entropy than GUID v4 (128 bits vs 122 bits)
No embedded timestamp (reduces predictability and improves strength)
Self-contained; does not use any packages

Usage features:

High performance, with minimal allocations
16 bytes in size; 22 characters as a string
Always starts with a letter (can be used as-is for programming language variable names)
URL-safe
Can be validated, parsed, and compared
Can be created from and converted to byte arrays
UTF-8 encoding support
JSON serialization support
TypeConverter support
Debug support (displays as string in the debugger)

Nuget

Yes, you can also find DUID on nuget. Look for the package named fynydd.duid.

Usage

Similar to Guid.NewGuid(), you can generate a new DUID by calling the static NewDuid() method:

var duid = Duid.NewDuid();

This will produce a new DUID, for example: aZ3x9Kf8LmN2QvW1YbXcDe. There are a ton of overloads and extension methods for converting, validating, parsing, and comparing DUIDs.

Here are some examples:

// Represents an empty DUID (all zeros); "AAAAAAAAAAAAAAAAAAAAAA"
var emptyDuid = Duid.Empty;

// Get a string value for a DUID
var duid = Duid.NewDuid();
var duidString = duid.ToString();

if (Duid.TryParse("aZ3x9Kf8LmN2QvW1YbXcDe", out var duid)
{
    // Successfully parsed DUID
}

if (Duid.IsValidString("aZ3x9Kf8LmN2QvW1YbXcDe"))
{
    // Successfully validated
}

if (duid1 == duid2)
{
    // Comparison works as expected
}

There is also a JSON converter for System.Text.Json that provides seamless serialization and deserialization of DUIDs:

var options = new JsonSerializerOptions();
options.Converters.Add(new DuidJsonConverter());

var user = new User
{
    Id = Duid.NewDuid(),
    FirstName = "Turd",
    LastName = "Ferguson"
};

var json = JsonSerializer.Serialize(user, options);

/*
    json =
    {
        id: "xw5x7Kf6LmN3QvW1YbXcc0",
        firstName: "Turd",
        lastName: "Ferguson"
    }
*/

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Open source software Subtopics : Security Subtopics : Cryptography Subtopics : Software development

The .NET DUID

Key security features:

Usage features:

Nuget

Usage

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