Generate UUID v4

A 128-bit identifier that is almost entirely random — 122 bits come straight from the CSPRNG, with only the 4-bit version and 2-bit variant fields fixed. The default choice when you want a random, unguessable ID.

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Generated · 0 IDs

This ID

Length 36 chars

Bits 128 (122 random)

Collision risk negligible

Collision

1% collision chance after ≈ 326,915,130,069,136,007 IDs

Random part 122 random bits

Counted together All generated IDs

This is a whole-set estimate, not a per-ID chance. UUID v4 has no timestamp or counter, so every generated ID shares the same random space.

Validate and parse UUID v4

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About UUID v4

Use when: you need a random, unguessable ID and ordering does not matter — request IDs, idempotency keys, file names.

Avoid when: you want IDs that sort by creation time (use UUID v7 or ULID) or shorter URLs (use NanoID).

How it is generated

A v4 UUID is mostly raw randomness. You take 16 bytes from a CSPRNG, then overwrite six bits to mark the version and the RFC 9562 variant. Everything else — all 122 remaining bits — is random.

No timestamp, no node, no counter. Two v4 UUIDs minted a microsecond apart look nothing like each other; that’s the whole point.

01 Read 16 bytes from crypto.getRandomValues.
02 Set the high nibble of byte 6 to 0100 (version 4).
03 Set the top two bits of byte 8 to 10 (variant). Leave the remaining 122 bits alone.
04 Hex-encode with dashes after bytes 4, 6, 8, 10.

xxxxxxxx-xxxx-4xxx-Nxxx-xxxxxxxxxxxx
└──┬───┘ └─┬┘ │└┬┘ │└┬┘ └────┬─────┘
   │       │  │ │  │ │       └── 48 random bits (bytes 10..15)
   │       │  │ │  │ └────────── 12 random bits (low 12 of bytes 8..9)
   │       │  │ │  └──────────── variant "10" (top 2 bits of byte 8)
   │       │  │ └─────────────── 12 random bits (low 12 of bytes 6..7)
   │       │  └───────────────── version "4" (top nibble of byte 6)
   │       └──────────────────── 16 random bits (bytes 4..5)
   └────────────────────────── 32 random bits (bytes 0..3)

Total: 122 random bits + 6 fixed bits (4 version + 2 variant).

All of this runs in your browser. Random bytes come from crypto.getRandomValues, timestamps come from the system clock, and nothing about the generated ID leaves the tab.