UUID Generator
Generate random v4 UUIDs. Runs entirely in your browser — nothing is sent to a server.
- Click "Generate" to create UUIDs
What is a UUID and Why Use UUID v4 for Unique Identifiers?
A UUID (Universally Unique Identifier), also known as a GUID (Globally Unique Identifier) in Microsoft ecosystems, is a 128-bit identifier that is unique across space and time. UUIDs are the industry standard for generating unique IDs in distributed systems where a central authority isn't available. The format is xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx — 32 hex digits separated by 4 hyphens.
UUID Versions Explained
- UUID v1 — Based on timestamp and MAC address. Guarantees uniqueness but leaks hardware identity and creation time. Rarely used in modern applications.
- UUID v4 (this tool) — Randomly generated using a CSPRNG. 122 bits of randomness yield 5.3 — 10—6 possible values — making collisions statistically impossible (you'd need to generate 1 billion UUIDs per second for 86 years to have a 50% chance of one collision).
- UUID v5 — Deterministic, generated by hashing a namespace + name with SHA-1. Same input always produces the same UUID. Useful for consistent ID generation.
- UUID v7 (new) — Time-ordered UUIDs that combine timestamp and randomness. Sortable by creation time, making them excellent for database primary keys.
Common Use Cases for UUID v4 in Software Development
- Database primary keys — UUIDs as primary keys in PostgreSQL (
uuidtype), MySQL, MongoDB, and DynamoDB avoid sequential ID enumeration attacks - Session identifiers — Web application sessions, shopping carts, and temporary tokens
- API request correlation IDs — Track requests across microservices with a unique
X-Request-IDheader - Distributed systems — Generate unique IDs on multiple servers without coordination or a central ID authority
- File naming — Unique filenames for user uploads to prevent overwriting (
a3f4b2c1-...-image.png) - Message queues — Unique message IDs in Kafka, RabbitMQ, SQS for idempotency and deduplication
UUID v4 vs Auto-Increment IDs vs ULID
- Auto-increment IDs — Sequential, predictable, requires a central database. Leaks record count and creation order. Not suitable for distributed systems.
- UUID v4 — Random, globally unique, no coordination needed. Downside: not sortable by time, poor database index locality on B-tree indexes.
- ULID — Lexicographically sortable, timestamp-prefixed, compatible with UUID storage. Better database performance than random UUIDs.
Frequently Asked Questions
This tool uses the browser's crypto.randomUUID() API to generate version 4 UUIDs with cryptographically secure randomness. Each UUID has 122 random bits formatted as 32 hexadecimal characters in the pattern xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx. Everything runs in your browser — no data is sent to any server.
With 122 bits of randomness, there are over 5.3 x 10^36 possible UUID v4 values. You would need to generate about 2.71 x 10^18 UUIDs (2.71 quintillion) for a 50% collision probability. In practice, generating 1 billion UUIDs per second for 86 years would give only a 50% chance of one duplicate.
UUID (Universally Unique Identifier) and GUID (Globally Unique Identifier) are the same thing — a 128-bit identifier. UUID is the standard term defined in RFC 4122 and used across platforms. GUID is Microsoft's term used in Windows, .NET, and SQL Server. Both follow the same format: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx.
UUID v4 is purely random and ideal when you need unique identifiers without time ordering. UUID v7 (proposed in RFC 9562) embeds a Unix timestamp, making it time-sortable and better for database primary keys since it maintains B-tree index locality. Use v7 for database IDs and v4 for correlation IDs or tokens.
Yes. All UUIDs are generated entirely in your browser using the Web Crypto API. No UUIDs are sent to any server or stored anywhere. The cryptographic randomness ensures UUIDs are unpredictable. However, UUID v4 should not be used as a security token — use dedicated CSRF tokens or session IDs for authentication purposes.