A UUID (Universally Unique Identifier) is a 128-bit identifier standardized as RFC 4122. It is represented as 32 hexadecimal digits in the format xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx. UUIDs are designed to be unique across space and time without a central authority to coordinate generation.

What is the difference between UUID and GUID?

GUID (Globally Unique Identifier) is Microsoft's implementation of UUID. They are technically the same format. GUID is the term used in Windows, .NET, and SQL Server, while UUID is the term used in the RFC standard and most other environments (Linux, Java, databases).

Can I use UUID as a database primary key?

Yes, UUID is widely used as a primary key. Benefits: globally unique across distributed systems, no auto-increment reveals record count, safe to generate client-side. Downsides: 16 bytes vs 4-8 bytes for an integer, random UUIDs cause index fragmentation in B-tree indexes. UUID v7 (ordered) solves the fragmentation issue.

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UUID Generator Online

Generate cryptographically random v4 UUIDs instantly with this free online UUID generator. Bulk generate up to 100 UUIDs at once, copy individually or all together with one click, and download as a text file. Options include uppercase formatting, hyphen removal, and wrapping in curly braces for GUID-style output. This tool uses your browser's native crypto.randomUUID() API — the gold standard for cryptographically secure random ID generation. All UUIDs are generated entirely in your browser. Nothing is sent to a server. Works offline, no signup required.

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How to use the UUID generator

UUIDs (or GUIDs) are 128-bit identifiers used as primary keys, request IDs, idempotency tokens, and feature-flag identifiers. The generator produces RFC 4122 v4 UUIDs (random) by default — cryptographically random via crypto.getRandomValues(), generated entirely in your browser. No collisions in practice; no network calls.

1. Click "Generate" for a single UUID, or set a count (1–1000) to produce a batch for test fixtures or seed data.
2. Pick the format: hyphenated (550e8400-e29b-41d4-a716-446655440000), no hyphens, uppercase, or wrapped in braces for older Microsoft systems.
3. Copy a single UUID with one click, or "Copy all" for the full batch — separated by newlines or commas.
4. Download as a text or JSON file for larger batches headed into a database seeder or test suite.
5. Toggle UUIDv7 if you need a time-ordered ID (better B-tree index locality than v4) — newer apps should default to v7.

Common UUID mistakes to avoid

Using UUIDv4 for sortable primary keys. v4 is fully random — terrible for B-tree index locality, causes write hotspots in MySQL/Postgres. For new tables, use UUIDv7 (time-ordered) or a ULID.
Storing UUIDs as VARCHAR(36) when your DB has a native type. Postgres has uuid, MySQL 8 has UUID_TO_BIN() for binary 16-byte storage. Native types are 2.25× smaller and faster.
Using UUIDv1 (timestamp + MAC). Leaks the server's MAC address and clock — privacy and security concern. Stick to v4, v7, or ULID.
Treating UUIDs as secret tokens. A UUID is an identifier, not authentication. Don't use them as session tokens or API keys — use proper random secrets with proper entropy.
Generating UUIDs with Math.random(). Not cryptographically secure — collisions are theoretically possible across enough generations. Use crypto.randomUUID() (built-in to modern browsers and Node 14+).
Embedding UUIDs in user-facing URLs. Long, ugly, and unindexable by humans. Use a short slug or hash for shareable URLs; keep UUIDs as the internal ID.

Frequently Asked Questions

What is a UUID?

A UUID (Universally Unique Identifier), also called GUID (Globally Unique Identifier), is a 128-bit identifier formatted as 32 hex digits in 5 groups: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx. It is designed to be unique across distributed systems without a central coordinator. UUID is standardized in RFC 4122 and used in databases, APIs, file systems, and distributed architectures worldwide.

What is the difference between UUID v1, v4, and v5?

v1 — timestamp + MAC address. Unique but reveals when and where it was generated, which is a privacy risk.

v4 — 122 bits of pure randomness. The most commonly used version. No structure, no reversibility.

v5 — deterministic: given the same name and namespace, you always get the same UUID (uses SHA-1). Good for content-addressed identifiers.

v7 — new standard: timestamp-ordered v4. Solves index fragmentation in databases while keeping randomness.

Are v4 UUIDs truly unique?

Statistically, yes. A v4 UUID has 122 random bits. The probability of generating even a single collision requires producing approximately 2.71 quintillion UUIDs. For any real-world application, collisions are not a practical concern. This tool uses crypto.randomUUID() — a cryptographically secure random number generator — not Math.random().

UUID vs GUID — what is the difference?

They are the same format. GUID is Microsoft's term, used in Windows APIs, .NET, C#, and SQL Server. UUID is the RFC standard term, used in Linux, Java, Python, PostgreSQL, and most non-Microsoft ecosystems. Both are 128-bit identifiers in the same xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx format.

Should I use UUID as a database primary key?

UUIDs are excellent primary keys for distributed systems where you need to generate IDs on the client or across multiple services. Main benefits: globally unique, no ID enumeration attacks, client-generated. Main concern: random v4 UUIDs cause index fragmentation in MySQL/PostgreSQL B-tree indexes, which can harm write performance at scale. Solution: use UUID v7 (time-ordered) or ULID for high-write workloads.

How do I generate a UUID in JavaScript, Python, or Go?

JavaScript (browser): crypto.randomUUID()
JavaScript (Node.js 14.17+): require('crypto').randomUUID()
Python: import uuid; str(uuid.uuid4())
Go: import "github.com/google/uuid"; uuid.New().String()
PostgreSQL: SELECT gen_random_uuid();
MySQL: SELECT UUID();

UUID Generator Online

How to use the UUID generator

Common UUID mistakes to avoid

Frequently Asked Questions

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