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How to Use
- 1Set the count using the input field to generate one or multiple UUIDs at once (up to 50). Bulk generation is useful for seeding databases, provisioning test accounts, or creating batches of unique identifiers for import files.
- 2Click Generate to create new version 4 UUIDs. Each UUID is produced using the Web Crypto API (crypto.randomUUID where available, with crypto.getRandomValues as fallback), ensuring cryptographically secure randomness.
- 3Click any individual UUID in the list to copy it to your clipboard. A toast notification confirms the copy, so you can immediately paste it into your code, database query, or configuration file.
- 4Use the Copy All button to copy the entire batch as a newline-separated list — ideal for pasting into CSV files, SQL INSERT statements, or test fixture files that require multiple unique identifiers.
- 5Click Generate again at any time for a completely fresh set. Previously generated UUIDs are replaced — if you need to preserve them, copy before regenerating.
- 6Each UUID follows the standard RFC 9562 format (xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx) with the version nibble set to 4 and the variant bits set to 10xx, making them universally recognizable as v4 UUIDs.
About UUID Generator
The UUID Generator creates version 4 universally unique identifiers using the browser's Web Crypto API — specifically crypto.randomUUID() in modern browsers, with a fallback to crypto.getRandomValues() for older environments. This provides the same quality of cryptographic randomness used by TLS handshakes, encryption key generation, and authentication tokens. Unlike implementations that rely on Math.random(), which is a pseudorandom number generator with a predictable seed, Web Crypto randomness is sourced from your operating system's entropy pool and is suitable for security-sensitive applications.
A UUID (Universally Unique Identifier) is a 128-bit value standardized by RFC 9562 (which superseded RFC 4122 in 2024). Version 4 UUIDs use 122 bits of random data plus 6 fixed bits that encode the version (0100) and variant (10xx). The resulting identifier is formatted as 32 hexadecimal digits in five hyphen-separated groups: 8-4-4-4-12. Despite the fixed bits, the 122-bit random space yields approximately 5.3 × 10^36 possible values — meaning you could generate one billion UUIDs per second for 85 years before reaching a 50% probability of a single collision.
UUIDs are the de facto standard for distributed identifier generation because they require no central coordination. In microservices architectures, each service can independently generate UUIDs for database records, API resources, event messages, and correlation IDs without risk of collision. PostgreSQL has native UUID support with the uuid-ossp and pgcrypto extensions, MySQL supports UUID() as a built-in function, and MongoDB uses 12-byte ObjectIDs that serve a similar (though not identical) purpose. When used as primary keys, UUIDs enable seamless database merges, cross-region replication, and multi-tenant isolation.
In web development, UUIDs appear everywhere: as session identifiers in authentication flows, idempotency keys in payment APIs (Stripe recommends UUID v4 for this), request correlation IDs in distributed tracing systems like Jaeger and Zipkin, temporary file names for upload processing, and unique component keys in React rendering. Their unpredictability also makes them suitable as unguessable resource identifiers in URL paths — though for truly secret tokens, additional entropy and server-side validation should be layered on top.
The bulk generation feature produces up to 50 UUIDs at once, each independently generated with full cryptographic randomness. This is practical for developers seeding test databases, creating fixture files for automated testing, populating CSV import templates, or generating batches of identifiers for data migration scripts. Each UUID in the batch is guaranteed to be unique (within the astronomical collision probability of v4) and can be directly used in SQL INSERT statements, JSON fixtures, or environment configuration files.
It is worth understanding how UUID v4 compares to other versions. UUID v1 combines a timestamp with the machine's MAC address, which guarantees uniqueness but leaks information about when and where the UUID was generated — a privacy concern that led to its declining use. UUID v3 and v5 are deterministic, hashing a namespace and name with MD5 or SHA-1 respectively — useful when you need reproducible identifiers from known inputs. UUID v7 (introduced in RFC 9562) is a newer time-ordered format that combines a Unix timestamp prefix with random bits, offering the sortability of v1 with the privacy of v4. For most general-purpose use cases today, v4 remains the most widely adopted choice due to its simplicity and broad library support.
Frequently Asked Questions
What is a UUID and how is it different from a GUID?
A UUID (Universally Unique Identifier) and a GUID (Globally Unique Identifier) are the same thing — both refer to a 128-bit identifier standardized by RFC 9562. The term GUID is commonly used in Microsoft ecosystems (.NET, SQL Server, Windows COM), while UUID is the standard term used in RFCs, Linux, PostgreSQL, and most programming languages. The format, generation algorithm, and collision probability are identical regardless of which name is used.
Are these UUIDs cryptographically secure?
Yes. UUIDs are generated using the Web Crypto API (crypto.randomUUID or crypto.getRandomValues), which draws randomness from your operating system's cryptographic entropy pool — the same source used for TLS key generation and disk encryption. This is fundamentally different from Math.random(), which uses a deterministic pseudorandom algorithm that can be predicted if the seed is known. Web Crypto randomness is suitable for session tokens, idempotency keys, and security-sensitive identifiers.
What is the difference between UUID v4 and other UUID versions?
UUID v4 is based entirely on cryptographic random numbers (122 random bits). UUID v1 uses a timestamp and MAC address, which guarantees ordering but leaks device identity. UUID v3 and v5 are deterministic — they hash a namespace plus a name using MD5 or SHA-1, always producing the same UUID for the same input. UUID v7 (new in RFC 9562) combines a 48-bit Unix millisecond timestamp with random bits, offering time-based sorting while preserving privacy. For most applications that need unpredictable, unique identifiers, v4 is the standard choice.
Can two UUID v4 values ever collide?
The mathematical probability is approximately 1 in 2^122 (about 5.3 × 10^36). To put this in perspective, you would need to generate 1 billion UUIDs per second for about 85 years to reach a 50% probability of finding a single duplicate. In practice, UUID v4 collisions have never been documented in any real-world system. The probability is so low that software architectures universally treat v4 UUIDs as unique without additional verification.
Should I use UUIDs as database primary keys?
UUIDs work well as primary keys in distributed systems, multi-tenant applications, and microservices architectures because they can be generated independently on any node without coordination. However, random UUIDs (v4) have a drawback in B-tree indexes: their randomness causes index page splits, increasing write amplification and fragmentation. For write-heavy workloads, consider UUID v7 (time-ordered) or ULID, which maintain sortability. PostgreSQL's uuid type stores UUIDs as 16 bytes (more compact than the 36-character string), and most modern databases have efficient native UUID support.
How do UUIDs compare to auto-incrementing integer IDs?
Auto-incrementing integers are compact (4 or 8 bytes vs. 16 bytes), naturally sorted, and index-friendly — making them faster for range queries and joins. However, they require a central authority (the database sequence), leak information about record count and creation order, and cause conflicts during database merges or distributed generation. UUIDs trade storage efficiency for independence: any client, server, or service can generate them without coordination, making them ideal for distributed systems, offline-first apps, and API-first architectures.
What is UUID v7 and should I use it instead of v4?
UUID v7, standardized in RFC 9562 (May 2024), embeds a 48-bit Unix millisecond timestamp in the most significant bits, followed by random data. This makes v7 UUIDs naturally time-sortable while still being unique and reasonably unpredictable. They perform significantly better as database primary keys because their monotonic ordering avoids the B-tree fragmentation caused by random v4 UUIDs. If your application benefits from chronological ordering (event logs, message queues, time-series data), v7 is the better choice. For general-purpose opaque identifiers where ordering does not matter, v4 remains perfectly suitable.
Are generated UUIDs stored or sent to a server?
No. All UUID generation happens entirely in your browser using the Web Crypto API. No data is transmitted to any server, stored in cookies, or logged. The generated UUIDs exist only in the page's memory and your clipboard (if you copy them). Once you close or navigate away from the tab, they are gone. There is no server-side component, no analytics on generated values, and no persistence of any kind.
Can I use UUIDs in URLs?
Yes, and this is a common pattern. UUIDs in URLs (e.g., /users/550e8400-e29b-41d4-a716-446655440000) serve as unguessable resource identifiers, preventing users from iterating through sequential IDs to access unauthorized resources. However, UUIDs alone should not be your only access control — always enforce authorization on the server side. For shorter URLs, consider encoding UUIDs in base62 or base64url (22 characters instead of 36), or using purpose-built short ID libraries like nanoid or KSUID.