Generate UUID (GUID) in C#

UUID v4 - Random (all .NET versions)

// Available in all .NET versions - zero dependencies
Guid id = Guid.NewGuid();
Console.WriteLine(id.ToString()); // → "550e8400-e29b-41d4-a716-446655440000"

UUID v7 - Time-ordered (.NET 9+)

// .NET 9+ - built-in UUID v7 (time-ordered)
// IDs generated later always sort after earlier ones
Guid id = Guid.CreateVersion7();
Console.WriteLine(id.ToString()); // → "018e8f6a-1b2c-7d3e-9f4a-5b6c7d8e9f0a"

// With explicit timestamp
Guid idWithTs = Guid.CreateVersion7(DateTimeOffset.UtcNow);

Format specifiers

Guid id = Guid.NewGuid();

// "D" (default) - with hyphens
Console.WriteLine(id.ToString("D")); // f47ac10b-58cc-4372-a567-0e02b2c3d479

// "N" - no hyphens (32 chars)
Console.WriteLine(id.ToString("N")); // f47ac10b58cc4372a5670e02b2c3d479

// "B" - with braces
Console.WriteLine(id.ToString("B")); // {f47ac10b-58cc-4372-a567-0e02b2c3d479}

// "X" - hex with 0x prefix components
Console.WriteLine(id.ToString("X")); // {0xf47ac10b,0x58cc,0x4372,{0xa5,0x67,...}}

1. ASP.NET Core middleware - request tracing

public class RequestIdMiddleware
{
    private readonly RequestDelegate _next;

    public RequestIdMiddleware(RequestDelegate next) => _next = next;

    public async Task InvokeAsync(HttpContext context)
    {
        var requestId = Guid.NewGuid().ToString("N"); // no hyphens for headers
        context.Items["RequestId"] = requestId;
        context.Response.Headers["X-Request-ID"] = requestId;
        await _next(context);
    }
}

// Register in Program.cs:
// app.UseMiddleware<RequestIdMiddleware>();

2. EF Core entity with GUID primary key

using System.ComponentModel.DataAnnotations;

public class Order
{
    [Key]
    public Guid Id { get; set; } = Guid.NewGuid(); // auto-assigned on creation

    public string CustomerName { get; set; } = string.Empty;
    public DateTime CreatedAt  { get; set; } = DateTime.UtcNow;
}

// EF Core automatically maps Guid to the native UUID/uniqueidentifier column type

3. Azure Service Bus message ID

using Azure.Messaging.ServiceBus;

var client = new ServiceBusClient(connectionString);
var sender = client.CreateSender("orders");

var message = new ServiceBusMessage(JsonSerializer.SerializeToUtf8Bytes(order))
{
    MessageId      = Guid.NewGuid().ToString(), // unique message ID
    CorrelationId  = correlationId,
    ContentType    = "application/json",
};

await sender.SendMessageAsync(message);

How do I generate a UUID in C#?

System.Guid.NewGuid() returns a random v4 GUID built into .NET, with no extra packages. Call .ToString() for the canonical 36-character form, or .ToString('N') for 32 hex characters without hyphens. For UUID v7, use Guid.CreateVersion7() on .NET 9 or later.

Is Guid.NewGuid() cryptographically secure?

Not guaranteed. Guid.NewGuid() produces a random v4 GUID via the OS GUID generator (UuidCreate on Windows), which Microsoft does not document as cryptographically secure. For session tokens, API keys, or other secrets, use System.Security.Cryptography.RandomNumberGenerator instead.

What is the difference between UUID v4 and v7 in C#?

UUID v4 (Guid.NewGuid() or equivalent) is fully random and not sortable. UUID v7 embeds a millisecond timestamp for chronological sorting (RFC 9562). Use v4 for general-purpose IDs; use v7 for database primary keys at scale.

Do I need to install a package for UUID generation in C#?

No additional package is required for basic v4 generation in C#. Check the Installation section for version-specific notes.

How do I validate a UUID string in C#?

Use the platform's UUID parse/validation function, or test against the RFC 4122 regex: /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i. Always validate external input at API boundaries.

Should I use UUIDs as database primary keys in C# applications?

UUIDs work well as primary keys for distributed systems. Prefer native UUID/BINARY(16) column types over VARCHAR(36). For very large tables, consider UUID v7 for better B-tree insert locality.

Can I generate UUIDs in C# without a network connection?

Yes. UUID generation uses local OS entropy sources and does not require network access. Each call is independent and thread-safe on modern platforms.

What output formats are available in C#?

The standard hyphenated lowercase string (36 chars) is the default. Most APIs also support 32-char hex (no hyphens) and 16-byte binary formats. Use string format for APIs and binary for database storage.

What RFC standards apply to C# UUID generation?

Version 4 UUIDs follow RFC 4122. UUID v7 follows RFC 9562 (May 2024). Ensure your chosen method produces compliant version and variant bits.

When should I avoid UUID v1?

Avoid UUID v1 in security-sensitive contexts - it embeds MAC address and timestamp information. Prefer v4 (Guid.NewGuid() or equivalent) unless you need legacy Cassandra timeuuid compatibility.