What is the difference between UUID v4 and v7?

V4 is random and contains no timestamp. V7 starts with a 48-bit Unix millisecond timestamp. This generator uses a 12-bit counter inside that millisecond and 62 random trailing bits. Canonical v7 strings sort by their embedded timestamp, which can improve index locality in some databases; actual insert speed and index size depend on the database and workload. Within this tab, the counter orders values while the clock advances normally. Counter exhaustion refuses another value until the clock advances, and a backwards clock or a different tab is outside that ordering guarantee.

How do I validate a UUID or decode a v7 timestamp?

Paste the value in the inspector. It accepts 32 hexadecimal characters or complete 8-4-4-4-12 groups, optionally enclosed in balanced braces, and accepts upper or lower case. A readable representation is reported separately from a recognized version and variant. Nil and Max have special labels. Only an RFC-variant v7 gets an embedded timestamp display; the timestamp does not prove when or by whom the value was made. V4 has no timestamp to extract.

Can I generate UUIDs in bulk or download the list?

Use the count buttons for 1, 5, 25, 100 or 1,000 identifiers in v4 or v7. Copy all copies one UUID per line, and Download TXT saves the same formatted list with a final newline. Each row also has its own Copy button. V5 produces one deterministic result for one namespace/name pair; asking for duplicates would not create new identifiers.

What are the odds of a UUID collision?

For independent uniformly random v4 values there are 2^122 possible random-bit combinations. The birthday approximation reaches a 50% chance of a duplicate near 2.7 × 10^18 generated values; no finite batch proves global uniqueness. V7 has a different timestamp/counter/random layout and depends on clock behavior, so the v4 estimate does not describe it. V5 deliberately repeats for the same namespace and name and uses SHA-1, whose collision resistance is not suitable for security-sensitive proof of identity.

Are UUIDs passwords, API secrets or authentication tokens?

Use a purpose-built password or secret generator for those jobs. V4 draws secure randomness, but a UUID is an identifier and does not implement an application’s token lifecycle. V7 exposes its timestamp, v5 is predictable from its inputs, and Nil and Max are fixed constants.

UUID v7 Generator

Generate UUID v7 values carrying the device’s Unix millisecond timestamp. This page opens V7 with a five-value batch. Copy or download the list, or paste a value into the inspector to read its embedded time.

Version 7 · timestampReady

Version

How many

Format

Validate and inspect a UUID

Check the representation, version and variant. For an RFC v7, read the embedded timestamp. This cannot prove uniqueness, origin or authenticity.

UUID

Formatting, count, version and a valid namespace can be remembered on this device. Names, generated UUIDs and inspection input are not saved. Page presets preserve remembered choices until you explicitly change each setting.

Common questions

What is the difference between UUID v4 and v7?: V4 is random and contains no timestamp. V7 starts with a 48-bit Unix millisecond timestamp. This generator uses a 12-bit counter inside that millisecond and 62 random trailing bits. Canonical v7 strings sort by their embedded timestamp, which can improve index locality in some databases; actual insert speed and index size depend on the database and workload. Within this tab, the counter orders values while the clock advances normally. Counter exhaustion refuses another value until the clock advances, and a backwards clock or a different tab is outside that ordering guarantee.
How do I validate a UUID or decode a v7 timestamp?: Paste the value in the inspector. It accepts 32 hexadecimal characters or complete 8-4-4-4-12 groups, optionally enclosed in balanced braces, and accepts upper or lower case. A readable representation is reported separately from a recognized version and variant. Nil and Max have special labels. Only an RFC-variant v7 gets an embedded timestamp display; the timestamp does not prove when or by whom the value was made. V4 has no timestamp to extract.
Can I generate UUIDs in bulk or download the list?: Use the count buttons for 1, 5, 25, 100 or 1,000 identifiers in v4 or v7. Copy all copies one UUID per line, and Download TXT saves the same formatted list with a final newline. Each row also has its own Copy button. V5 produces one deterministic result for one namespace/name pair; asking for duplicates would not create new identifiers.
What are the odds of a UUID collision?: For independent uniformly random v4 values there are 2^122 possible random-bit combinations. The birthday approximation reaches a 50% chance of a duplicate near 2.7 × 10^18 generated values; no finite batch proves global uniqueness. V7 has a different timestamp/counter/random layout and depends on clock behavior, so the v4 estimate does not describe it. V5 deliberately repeats for the same namespace and name and uses SHA-1, whose collision resistance is not suitable for security-sensitive proof of identity.
Are UUIDs passwords, API secrets or authentication tokens?: Use a purpose-built password or secret generator for those jobs. V4 draws secure randomness, but a UUID is an identifier and does not implement an application’s token lifecycle. V7 exposes its timestamp, v5 is predictable from its inputs, and Nil and Max are fixed constants.

UUID v4 uses secure browser randomness. UUID v7 includes the device-clock timestamp, a counter and random bits; clock rollback and other tabs are outside its ordering guarantee. UUID v5 follows the SHA-1 namespace/name construction and is deterministic, not secret. Inspection checks representation and layout, not uniqueness or authenticity.