UUID & ULID Bulk Generator
Generate UUID v4s or ULIDs in bulk with formatting options, and validate any ID you paste — backed by cryptographically strong randomness.
Interactive Client Prototype Sandbox
Disclaimer: This free tool is provided “as is,” without warranties of any kind, and is for general informational purposes only — not professional, legal, financial, medical, tax, or engineering advice. Results may contain errors; verify anything important independently and use at your own risk. We accept no liability for any loss or damage arising from its use. See our Terms of Use for details.
Step-by-Step Guide
Choose UUID v4 or ULID, set a count (1 to 1,000), and configure formatting options: toggle hyphens on or off, and switch between lowercase and uppercase output. Press Generate to produce the batch. Click any individual ID in the list to copy it, or use Copy All to grab the entire set at once. The built-in validator accepts any ID pasted into the field and tells you whether it is a valid UUID v4, a valid ULID, or neither.
UUID v4 vs ULID — which to choose
UUID v4 identifiers are 128-bit random values, formatted as 8-4-4-4-12 hexadecimal digits (e.g. f47ac10b-58cc-4372-a567-0e02b2c3d479). Version 4 means the bits are randomly generated, with a small number of fixed bits indicating the version. They are globally unique with overwhelming probability and have no inherent sort order.
ULID (Universally Unique Lexicographically Sortable Identifier) encodes 48 bits of millisecond-precision timestamp followed by 80 bits of randomness, producing a 26-character Crockford Base32 string (e.g. 01ARZ3NDEKTSV4RRFFQ69G5FAV). Because the timestamp comes first, ULIDs sort chronologically, which is valuable for database primary keys where insertion order matters for performance.
Generate 10 UUID v4s with hyphens and lowercase: each is 36 characters like '550e8400-e29b-41d4-a716-446655440000'. Generate 10 ULIDs: each is 26 characters like '01ARZ3NDEKTSV4RRFFQ69G5FAV'. Paste one into the validator to confirm it is recognized as a valid UUID or ULID.
Who it's for
Developers, database designers, testers, and anyone needing unique identifiers.
Core Features
- Bulk-generate UUID v4s or time-sortable ULIDs (up to 1000 at once).
- Toggle uppercase and hyphens; copy a single ID or all of them.
- Built-in validator that recognizes UUIDs and ULIDs.
- Uses crypto.randomUUID / getRandomValues — unguessable and offline.
🛡️ No tracking — your inputs, keys, and details never leave this client sandbox.
What is a UUID and why do databases use them?
A UUID (Universally Unique Identifier) is a 128-bit value designed to be unique across all systems and all time without requiring coordination between generators. UUID v4, the random variant, relies on the astronomical improbability of two randomly generated 128-bit numbers being the same — the chance is roughly 1 in 10^36 for any given pair. Databases use UUIDs as primary keys when rows are created across distributed systems (multiple servers, mobile clients, offline-first apps) and need to merge into a single table without ID conflicts.
What makes ULIDs better for database performance?
Standard UUID v4 values are random, which means consecutive inserts go to random positions in a B-tree index, causing page fragmentation and frequent index rebuilds — a performance problem at high insert rates. Because ULIDs encode a timestamp as their first 10 characters, consecutive inserts sort in approximate chronological order, keeping index pages mostly sequential. This is the same reason auto-incrementing integer IDs have historically been preferred for performance: ULID gives you global uniqueness without the sequential bottleneck of a centralized ID counter.
Are UUID v4s truly random and safe to use as public identifiers?
UUID v4s are generated from a cryptographically strong random source (crypto.randomUUID in browsers and crypto.getRandomValues in Node.js), making them unguessable and safe to use as identifiers in URLs. They are not sequential and provide no information about when or where they were created. Avoid using simple auto-incrementing integers as public-facing record IDs because enumeration attacks allow anyone to discover all records; UUID v4 avoids this.
What is the UUID without hyphens and when would I use it?
The 32-character format without hyphens (e.g., f47ac10b58cc4372a5670e02b2c3d479) is the same UUID, just stripped of the formatting dashes. Some systems and databases store UUIDs in a binary 16-byte column and accept the unhyphenated string as input. Others prefer the hyphenated form. The underlying value is identical; the hyphens are purely visual grouping aids.
UUIDs and ULIDs in practice
Picture this: a development team is building a multi-tenant SaaS product where users can create records on mobile clients while offline and later sync to a central server. If they use auto-incrementing integers as primary keys, two clients that both create a 'record #1047' while offline will collide on sync. The standard fix is to generate IDs on the client using a UUID v4 — a 128-bit random value that is globally unique with overwhelming probability, requiring no coordination with any server and revealing nothing about when or where it was created. This is the scenario UUIDs were designed for, and it plays out across distributed databases, event-sourcing systems, and offline-first apps every day.
UUID versions: which one to use
The UUID standard (RFC 4122) defines five versions. Version 1 encodes a MAC address and timestamp, making the generating device identifiable — a privacy concern. Versions 3 and 5 generate deterministic UUIDs from a namespace and a name using MD5 or SHA-1, useful for creating stable identifiers from known strings. Version 4 uses random bits and is the most commonly used version because it requires no special setup and reveals no information about its origin. A UUID v4 has 122 random bits (6 are fixed to identify version and variant), giving 2^122 ≈ 5.3 × 10^36 possible values — collisions are astronomically unlikely.
The ULID specification
ULID was proposed as an alternative to UUID v4 that retains the monotonically increasing property of sequential IDs while remaining globally unique and decentralized. A ULID encodes 48 bits of Unix millisecond timestamp (good until the year 10889) followed by 80 bits of cryptographic randomness, encoded in 26 Crockford Base32 characters. Multiple ULIDs generated in the same millisecond have the same timestamp prefix and random suffixes, but the spec defines an optional monotonic mode where the random component is incremented by 1 for each additional ID in the same millisecond, guaranteeing strict monotonicity even within the same process.
When not to use this tool
Bulk-generated UUIDs from a browser tool are suitable for seeding test databases, populating fixtures, or one-off migrations. For production systems, IDs should be generated at insert time by your application code using a cryptographically strong source (crypto.randomUUID in Node.js 14.17+, or a library like the uuid npm package). Generating IDs externally and pasting them into a production database is fine for testing but introduces a manual step that is easy to skip or repeat accidentally in a real workflow.