Free Bulk UUID Generator

Generate up to 500 random UUID v4 values instantly — locally in your browser, never sent to any server.

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What Is a UUID?

UUID stands for Universally Unique Identifier — a 128-bit label used to uniquely identify information in computer systems. A UUID is typically represented as 32 hexadecimal digits grouped in a pattern of 8-4-4-4-12, separated by hyphens: 550e8400-e29b-41d4-a716-446655440000. The format produces 2¹²⁸ possible values — approximately 340 undecillion unique identifiers — making the probability of a collision (two UUIDs being identical) astronomically small.

UUIDs are defined by the Open Software Foundation (OSF) and standardised in RFC 4122. They are widely used in databases, APIs, distributed systems, file systems, and software development to create unique record identifiers without requiring a central authority to assign them.

UUID vs GUID — What's the Difference?

In practice, UUID and GUID (Globally Unique Identifier) are the same thing. GUID is Microsoft's implementation of the UUID standard, and the terms are used interchangeably. You will see GUID in Microsoft documentation, SQL Server, Azure, and .NET applications, and UUID in the broader open-source and standards world. The format and generation algorithm are identical.

Some Microsoft tools display GUIDs with uppercase letters and sometimes include surrounding curly braces: {550E8400-E29B-41D4-A716-446655440000}. The UUID version on Unix and open-source systems is typically lowercase without braces. The format toggle on this tool lets you generate either form.

UUID Version 4 Explained

There are multiple UUID versions, each with a different generation strategy. The most commonly used in modern development is UUID v4:

  • UUID v1: Based on the current timestamp and the MAC address of the generating device. Reveals when and where it was created — potentially a privacy issue.
  • UUID v3: Name-based, generated by hashing a name and namespace with MD5. Deterministic — the same input always produces the same UUID.
  • UUID v4: Randomly generated — 122 bits of randomness, with 6 bits fixed for version and variant identification. This is the most widely used version today because it is simple, fast, and requires no network access or persistent state.
  • UUID v5: Like v3 but uses SHA-1 hashing instead of MD5.

UUID v4 is the default for most modern databases, ORMs, and backend frameworks. This tool generates UUID v4 using the browser's crypto.getRandomValues() API — a cryptographically secure random number generator — ensuring genuinely random output.

Use Cases for UUIDs in Databases and APIs

UUIDs solve a fundamental problem in distributed and multi-tenant systems: how do you create a unique identifier for a record without a central database sequence assigning it? With auto-incrementing integers, you need to insert a record to get its ID. With UUIDs, you can generate the ID client-side (in the browser or application) before the record even exists — enabling offline-first applications, optimistic UI updates, and conflict-free multi-master database replication.

Common development use cases for bulk UUID generation include:

  • Database seeding: Generating test data with pre-known IDs for development and testing environments.
  • API testing: Populating Postman, Insomnia, or cURL requests with valid UUID values for endpoints that require UUID parameters.
  • File naming: Using UUIDs as unique filenames for uploaded files prevents collisions and removes the need to check for existing names.
  • Session tokens: UUIDs are used as session identifiers, API keys, and tokens in authentication systems.
  • Correlation IDs: In distributed tracing, each request is tagged with a UUID that flows through all microservices so logs from different services can be correlated.
  • Idempotency keys: Payment APIs like Stripe use UUID-like keys to ensure that duplicate requests (e.g., from a retry) do not result in duplicate charges.

Frequently Asked Questions

UUID v4 has 2¹²² possible values — approximately 5.3 × 10³⁶. The probability of generating two identical UUIDs is so small it is effectively impossible in practice. You would need to generate approximately 2.71 × 10¹⁸ UUIDs before the probability of a collision reaches 50% — that is 2.71 quintillion UUIDs. For all practical purposes, UUID v4 values can be treated as globally unique.

Yes. This tool uses window.crypto.getRandomValues(), which is a cryptographically secure pseudo-random number generator (CSPRNG). The generated UUIDs are never sent to any server — all computation happens locally in your browser. The generated values are suitable for use as session identifiers, API keys, and other security-sensitive identifiers.

Both have trade-offs. Auto-increment integers are compact (4–8 bytes vs 16 bytes for UUID), index efficiently, and are human-readable. UUIDs are better for distributed systems (no central sequence), prevent ID enumeration attacks (users cannot guess adjacent record IDs), and enable client-side ID generation. For single-server applications, integers are often sufficient. For APIs, multi-tenant systems, and distributed databases, UUID v4 is usually preferred.

UUID v4 follows RFC 4122, which specifies that the 13th character (version field) must be "4" and the 17th character (variant field) must be one of "8", "9", "a", or "b". These fixed bits encode the version and variant of the UUID into the value itself, allowing parsers to identify the type without external metadata. The remaining 122 bits are random, giving UUID v4 its entropy.

Yes. PostgreSQL has a native UUID data type that stores UUIDs efficiently as 16 bytes. MySQL and MariaDB support UUIDs as CHAR(36) or can store them as BINARY(16) for better performance. Most ORMs — Django, Rails, Laravel, Prisma, SQLAlchemy — have built-in support for UUID primary keys. The main downside is slightly worse index performance compared to integers due to random ordering, which can be mitigated using UUID v7 (time-sortable) or ULID.

This tool generates up to 500 UUIDs at once — sufficient for the vast majority of development tasks including database seeding, test fixture generation, and API testing. All 500 are generated in milliseconds since the computation is entirely in-memory with no network requests. For truly bulk generation (millions of UUIDs), use a command-line tool or a language's built-in UUID library.

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