UUID / ULID Generator

What is UUID / ULID Generator?

UUID / ULID Generator is a browser-based tool that creates unique identifiers — random UUID v4, time-ordered UUID v7, or ULID — either one at a time or in bulk. Every value is produced locally using your browser's cryptographically secure random number generator, so the identifiers are suitable for real use, not just placeholders.

Unique identifiers are the backbone of distributed systems. Databases need primary keys that will not collide, message systems need to tag events, and services generating IDs independently must never accidentally produce the same one. UUIDs (Universally Unique Identifiers) solve this with 128-bit values that are astronomically unlikely to repeat, and ULIDs offer the same uniqueness while sorting by creation time.

The tool supports the formats you are most likely to need: UUID v4 for pure randomness, UUID v7 and ULID for time-ordered IDs that index efficiently in databases. Because generation happens entirely in your browser, nothing is uploaded — you can generate thousands of IDs offline.

Why use UUID / ULID Generator?

Generating IDs by hand or from an untrusted site is risky. You need identifiers that are genuinely unique and, for anything security-adjacent, unpredictable. This tool uses the browser's crypto-grade randomness, so the values are safe to use as real keys rather than throwaway test data, and bulk generation lets you seed a database or fixtures instantly.

Choosing the right format has real performance implications. Purely random UUID v4 values scatter across a database index, causing fragmentation on high-write tables. Time-ordered UUID v7 and ULID values sort chronologically, so new rows append near each other, dramatically improving insert performance and index locality. Being able to pick the format that fits your storage matters.

Local generation is a privacy and reliability benefit. You never depend on a remote service being up, and no third party ever sees the identifiers you create — which can matter when IDs are tied to real records. You can confirm zero network activity in the Network tab while generating.

Features

• Generate UUID v4 (random), UUID v7 (time-ordered), and ULID
• Produce a single ID or many in bulk
• Uses the browser's cryptographically secure random generator
• Time-ordered formats for better database index locality
• Copy all generated IDs at once
• Download the generated IDs as a text file
• Shows how many IDs were generated
• Runs entirely in your browser — no uploads, works offline

How to use UUID / ULID Generator

1. Choose the identifier format — UUID v4 for pure randomness, or UUID v7 / ULID for time-ordered IDs.
2. Enter how many IDs you want, from a single value up to the bulk limit.
3. Click Generate to produce the identifiers, which appear in the result panel.
4. Use "Copy all" to copy every ID to your clipboard, or download them as a text file.
5. Change the format or count and generate again whenever you need a fresh batch.

Common Mistakes

• Using random UUID v4 as a primary key on a high-write table: v4 values scatter across the index and cause fragmentation. Prefer time-ordered UUID v7 or ULID for database keys to keep inserts localized.
• Assuming UUIDs are secret or unguessable in a security sense: while v4 is random, UUIDs are identifiers, not secrets. Do not rely on a UUID alone as an unguessable capability token unless you understand its entropy.
• Expecting UUIDs to be short: a UUID is 36 characters with hyphens. If you need a compact URL-safe ID, ULID (26 chars) or a different scheme may suit better.
• Mixing formats in one table: storing a blend of v4 and v7 values in the same key column defeats the ordering benefit of v7. Pick one format per identifier column and stick with it.
• Treating ULID timestamps as precise clocks: the time component orders IDs and is millisecond-based, but it is not a substitute for a proper created_at timestamp with timezone handling.
• Regenerating IDs you have already assigned: once an ID is stored against a record, generating a new one does not update the record. Generate IDs at creation time, not repeatedly.

Developer Tips

• Default to UUID v7 or ULID for database primary keys — the time ordering keeps new rows clustered in the index and noticeably improves insert-heavy workloads compared to random v4.
• Use UUID v4 when you specifically want no time information leaked in the ID, such as tokens where creation time should not be inferable.
• Generate a bulk batch here to seed test fixtures or migrations quickly, then download them as a file to commit alongside your test data.
• Remember ULIDs are lexicographically sortable as plain strings, which is handy when your storage sorts keys as text and you want chronological order for free.
• Because generation is local and crypto-secure, these IDs are safe for production use — no need to route through a server just to get a unique value.

Frequently Asked Questions

What is the difference between UUID v4, UUID v7, and ULID?

UUID v4 is generated from random bits, so it carries no information about when it was created and its values are unordered. UUID v7 and ULID both embed a timestamp in their leading bits, which makes them sort chronologically while still being unique. UUID v7 follows the standard UUID format (36 characters with hyphens), while ULID uses a more compact 26-character encoding. For database keys, the time-ordered formats generally perform better; for pure randomness, v4 is the classic choice.

Are these UUIDs truly unique?

For practical purposes, yes. A UUID is a 128-bit value, and the number of possible values is so vast that the probability of generating the same random UUID twice is negligible even across billions of IDs. Time-ordered formats add a timestamp component that further reduces collision risk within the same instant. While no scheme guarantees mathematical impossibility of a collision, UUIDs are designed so that collisions are astronomically unlikely in any realistic system.

Why prefer a time-ordered ID for database keys?

Random UUID v4 values are spread uniformly across the key space, so consecutive inserts land in random positions within the database index. On high-write tables this causes index fragmentation and extra I/O. Time-ordered IDs like UUID v7 and ULID increase monotonically, so new rows append near each other, keeping the working set of the index small and improving insert throughput and cache locality. This is why many teams now default to v7 or ULID for primary keys.

Are the IDs generated on a server?

No. All identifiers are generated locally in your browser using the Web Crypto API's secure random number generator. Nothing is sent to a server, and no ID you generate is ever seen by a third party. You can verify this by opening your browser's Network tab while generating: there are zero outbound requests, and the tool continues to work even offline. This makes it safe to generate IDs that will be tied to real records.

Can I generate many IDs at once?

Yes. Set the count to generate a batch in a single click, up to the tool's bulk limit, then copy them all or download them as a text file. This is useful for seeding test fixtures, populating a migration, or pre-generating keys. Because everything runs in the browser with crypto-grade randomness, the bulk values are just as safe and unique as single ones — there is no quality trade-off in generating many at once.

Is a UUID safe to use as a security token?

A random UUID v4 has a large amount of entropy, so it is hard to guess, but UUIDs are fundamentally identifiers rather than secrets. Time-ordered formats (v7, ULID) intentionally encode the creation time, which makes them partly predictable and unsuitable as secret tokens. If you need an unguessable capability or session token, use a dedicated cryptographically random secret of appropriate length rather than relying on the ID format alone.

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