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UUID in C#

Production-ready implementation guide with CSPRNG-backed code snippets.

Generate UUID (GUID) in C#

System.Guid.NewGuid() is built into .NET — zero dependencies, returns a 16-byte value type. .NET 9 adds Guid.CreateVersion7() for time-ordered UUIDs natively.

Quick Reference

Method	Version	Sortable	Use Case
Guid.NewGuid()	v4	No	General purpose — session IDs, record IDs, API keys
Guid.CreateVersion7()	v7	Yes	.NET 9+ — time-ordered, database PKs
Guid.Parse()	any	—	Parse — throws on invalid input
Guid.TryParse()	any	—	Safe parse — returns bool, no exception

Primary Implementation

Production Ready

csharp snippet

// No using statements needed — System.Guid is in the global namespace

// Generate a GUID (UUID v4) — CSPRNG-backed, zero dependencies
Guid id = Guid.NewGuid();
Console.WriteLine(id);
// → f47ac10b-58cc-4372-a567-0e02b2c3d479

// Format specifiers
string standard  = id.ToString();        // "f47ac10b-58cc-4372-a567-0e02b2c3d479"
string noHyphens = id.ToString("N");     // "f47ac10b58cc4372a5670e02b2c3d479"
string braces    = id.ToString("B");     // "{f47ac10b-58cc-4372-a567-0e02b2c3d479}"
string parens    = id.ToString("P");     // "(f47ac10b-58cc-4372-a567-0e02b2c3d479)"

// Parse — throws FormatException on invalid input
Guid parsed = Guid.Parse("f47ac10b-58cc-4372-a567-0e02b2c3d479");

// Safe parse — no exception
if (Guid.TryParse("f47ac10b-58cc-4372-a567-0e02b2c3d479", out Guid result))
{
    Console.WriteLine($"Parsed: {result}");
}

// Check for empty/null GUID
if (id == Guid.Empty)
{
    Console.WriteLine("ID is empty");
}

// Generate multiple
var ids = Enumerable.Range(0, 5).Select(_ => Guid.NewGuid()).ToList();

All UUID Versions

UUID v4 — Random (all .NET versions)

csharp snippet

// 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+)

csharp snippet

// .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

csharp snippet

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,...}}

Real-World Use Cases

1. ASP.NET Core middleware — request tracing

csharp snippet

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

csharp snippet

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

csharp snippet

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);

Common Mistakes

✗

Calling ToString() without a format specifier

The default ToString() uses the "D" format (with hyphens, lowercase). Be explicit with the format specifier when the output format matters — e.g., ToString("N") for no hyphens.

✗

Using null checks instead of Guid.Empty

Guid is a value type — it can never be null (unless wrapped in Guid?). Use id == Guid.Empty to check for an uninitialized GUID, not a null check.

✗

Storing GUIDs as nvarchar(36) in SQL Server

SQL Server has a native uniqueidentifier type (16 bytes). EF Core maps Guid to it automatically. Using nvarchar(36) wastes space and loses index efficiency.

How It Works

Guid.NewGuid() calls the OS CSPRNG — BCryptGenRandom on Windows and /dev/urandom on Linux/macOS via .NET's platform abstraction layer.

Guid is a 16-byte value type (struct) stored on the stack. It implements IComparable, IEquatable, and IFormattable. Zero heap allocation per GUID.

Output Formats

ToString() / "D"

f47ac10b-58cc-4372-a567-0e02b2c3d479

"N" — no hyphens

f47ac10b58cc4372a5670e02b2c3d479

"B" — with braces

{f47ac10b-58cc-4372-a567-0e02b2c3d479}

Best Practices

✓

Use Guid type in C# — only convert to string at API/DB boundaries.

✓

Use Guid.TryParse() for user input — avoids exceptions on invalid strings.

✓

On .NET 9+, use Guid.CreateVersion7() for database PKs — sequential inserts.

Performance

.NET generates roughly 10–20 million GUIDs/second. Guid is a 16-byte value type — stack-allocated, zero heap pressure per GUID.

The ToString() call allocates a string on the heap. For high-throughput scenarios, use TryFormat() with a Span<char> to avoid allocations.

Installation

// No installation needed — System.Guid
// is part of the .NET base class library

Available in all .NET versions (.NET Framework 1.1+, .NET Core, .NET 5+). Guid.CreateVersion7() requires .NET 9+.

Security

Entropy source: OS CSPRNG — BCryptGenRandom on Windows, /dev/urandom on Linux/macOS. Cryptographically secure.

Suitable for session tokens, CSRF tokens, and API keys. Guid.Empty (00000000-0000-0000-0000-000000000000) is not a valid random GUID — never use it as an ID.