UUID generator

// v4, built in since Node 19 and in every current browser.
crypto.randomUUID();

// Web Crypto has no v7. 48-bit big-endian millisecond timestamp,
// then 74 random bits around the version and variant fields.
function uuidv7() {
  const b = crypto.getRandomValues(new Uint8Array(16));
  const ts = Date.now();
  b[0] = (ts / 2 ** 40) & 0xff;
  b[1] = (ts / 2 ** 32) & 0xff;
  b[2] = (ts / 2 ** 24) & 0xff;
  b[3] = (ts / 2 ** 16) & 0xff;
  b[4] = (ts / 2 ** 8) & 0xff;
  b[5] = ts & 0xff;
  b[6] = (b[6] & 0x0f) | 0x70;  // version 7
  b[8] = (b[8] & 0x3f) | 0x80;  // variant 10
  const h = [...b].map((v) => v.toString(16).padStart(2, "0")).join("");
  return `${h.slice(0,8)}-${h.slice(8,12)}-${h.slice(12,16)}-${h.slice(16,20)}-${h.slice(20)}`;
}

crypto.randomUUID() only ever produces v4, in the browser and on Node alike. Node does now ship a native v7 as randomUUIDv7() on node:crypto, added in 24.16.0 and 26.1.0, but there is still no v7 anywhere in the Web Crypto API.

import uuid

uuid.uuid4()          # random
uuid.uuid5(uuid.NAMESPACE_DNS, "example.com")   # name based, deterministic

# Python 3.14 added uuid6(), uuid7() and uuid8() to the standard library.
uuid.uuid7()

# On 3.13 and earlier v7 needs a library:
#   pip install uuid6
from uuid6 import uuid7
uuid7()

uuid.uuid4() draws from os.urandom, so it is cryptographically secure. uuid.uuid8() is documented as not using a CSPRNG by default, so it is not a drop-in replacement for uuid4().

-- v4, built in since PostgreSQL 13.
SELECT gen_random_uuid();

-- v7 is native from PostgreSQL 18.
SELECT uuidv7();

-- As a primary key, v7 keeps inserts at the right edge of the index
-- instead of scattering them the way v4 does.
CREATE TABLE orders (
  id          uuid        PRIMARY KEY DEFAULT uuidv7(),
  placed_at   timestamptz NOT NULL DEFAULT now(),
  total_cents integer     NOT NULL
);

import "github.com/google/uuid"

uuid.New()          // v4, panics on entropy failure
uuid.NewRandom()    // v4, returns an error instead
uuid.NewV7()        // v7, added in google/uuid v1.5.0

import java.util.UUID;

UUID.randomUUID();   // v4, backed by SecureRandom

// v7 is not in the JDK. java-uuid-generator, artifact
// com.fasterxml.uuid:java-uuid-generator:5.1.0
import com.fasterxml.uuid.Generators;
Generators.timeBasedEpochGenerator().generate();   // returns java.util.UUID

Guid.NewGuid();          // v4
Guid.CreateVersion7();   // v7, added in .NET 9

// Watch the byte order. Guid.ToByteArray() returns the first three
// fields little-endian, which is the classic mixed-endian GUID trap
// when moving values between .NET and anything else.
Guid.NewGuid().ToByteArray(bigEndian: true);

The mixed-endian layout is why a GUID can look different after a round trip through .NET.

# Linux, from the kernel
cat /proc/sys/kernel/random/uuid

# uuidgen, from util-linux
uuidgen --random     # v4
uuidgen --time       # v1

# Python one-liner, portable
python3 -c "import uuid; print(uuid.uuid4())"