GUID in C#

What is a GUID in C#

Guid.NewGuid() returns a version 4 GUID generated by the cryptographic provider. It is available in every .NET version and is the normal choice for entity keys, message ids and cache keys. The type is a struct, so a Guid field costs 16 bytes with no allocation.

.NET 9 added Guid.CreateVersion7(), which follows RFC 9562 and starts with a Unix millisecond timestamp — the variant you want when the column is clustered or indexed, because new rows land next to each other instead of scattering. The same release added an overload that takes a DateTimeOffset, so you can generate a v7 for a specific moment. GUIDs are written in five shapes: D (hyphenated), N (32 digits), B (braces), P (parentheses) and X (with 0x prefixes) — pick the one the consuming system expects.

How to

1. Call Guid.NewGuid() for a random v4 value.
2. On .NET 9+, call Guid.CreateVersion7() for a time-ordered value.
3. Use ToString("B") or ToString("N") to match the format the other side needs — the formatter above does the same for a whole list.

Use cases

• Entity Framework Core keys: assign the value in the model so the key exists before the INSERT.
• SQL Server UNIQUEIDENTIFIER columns, where NEWID() gives v4 and NEWSEQUENTIALID() a sequential value.
• Distributed systems and message ids, where each node must be able to mint an identifier without coordinating.

Compare GUID in C# with other formats

Code examples

Random v4

using System;

Guid id = Guid.NewGuid();
Console.WriteLine(id);            // 550e8400-e29b-41d4-a716-446655440000
Console.WriteLine(id.ToString("N"));  // 550e8400e29b41d4a716446655440000
Console.WriteLine(id.ToString("B"));  // {550e8400-e29b-41d4-a716-446655440000}

Time-ordered v7 (.NET 9+)

using System;

Guid v7 = Guid.CreateVersion7();
Console.WriteLine(v7);            // 019535d9-3df7-79fb-b466-fa907fa17f9e
Console.WriteLine(v7.Version);    // 7

// A specific moment, for backfills
Guid historical = Guid.CreateVersion7(
    new DateTimeOffset(2025, 1, 1, 0, 0, 0, TimeSpan.Zero));

Format specifiers

Guid g = Guid.NewGuid();

g.ToString("N");  // 32 digits, no hyphens
g.ToString("D");  // 8-4-4-4-12, the default
g.ToString("B");  // braces, the .NET config-file shape
g.ToString("P");  // parentheses
g.ToString("X");  // hexadecimal: 0x...

Parsing safely

if (Guid.TryParse(input, out Guid parsed))
{
    // well-formed and legal
}
else
{
    // reject the input instead of throwing

Frequently asked questions