Generator Tools

UUID Generator

Generate UUID v4 identifiers instantly. Bulk generation, one-click copy, and regenerate on demand.

Your data never leaves your browser — nothing is sent to any server.

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How to use
  1. 1

    Set the quantity

    Enter a number between 1 and 100 in the count input to control how many UUIDs are generated at once.

  2. 2

    Choose the case format

    Toggle the uppercase switch to generate UUIDs in uppercase (e.g., A1B2C3D4-...) or leave it off for the standard lowercase format.

  3. 3

    Copy individual UUIDs

    Click any UUID row or its copy icon to copy that single identifier to your clipboard.

  4. 4

    Copy all or regenerate

    Use 'Copy All' to copy every UUID separated by newlines. Click 'Regenerate' to create a fresh batch with the same settings.

FAQ (6)
What is a UUID v4?

UUID v4 (Universally Unique Identifier version 4) is a 128-bit identifier generated using cryptographically secure random numbers. It follows the format xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx, where '4' indicates the version and 'y' is one of 8, 9, a, or b. The probability of collision is astronomically low — roughly 1 in 2^122 — making it safe for use as a primary key without coordination between systems.

Are UUIDs generated in the browser secure?

Yes. This tool uses the Web Crypto API (crypto.randomUUID()), which relies on a cryptographically secure pseudorandom number generator (CSPRNG) provided by the operating system. The generated UUIDs are compliant with RFC 9562 and are suitable for database keys, session tokens, and distributed system identifiers.

What is the difference between UUID and GUID?

UUID (Universally Unique Identifier) and GUID (Globally Unique Identifier) refer to the same concept. UUID is the term used in the IETF RFC specification, while GUID is the term historically used by Microsoft. Both describe a 128-bit identifier in the same 8-4-4-4-12 hexadecimal format. In practice, they are interchangeable.

Can UUID v4 collisions actually occur?

While theoretically possible, a collision is extraordinarily unlikely. You would need to generate approximately 2.71 × 10^18 UUIDs (2.71 quintillion) to have a 50% chance of a single collision. For virtually all applications — including databases with billions of rows — UUID v4 can be treated as unique without any coordination or central authority.

Should I use uppercase or lowercase UUIDs?

RFC 9562 states that UUIDs should be output as lowercase but accepted case-insensitively. Lowercase is the most common convention in databases, APIs, and programming languages. Some legacy systems (notably older Microsoft tools) use uppercase. Choose one convention and be consistent across your system to avoid comparison bugs.

How does bulk UUID generation work?

This tool generates multiple UUIDs in a single batch by calling crypto.randomUUID() repeatedly. Each call produces an independent, cryptographically random UUID v4. You can generate up to 100 UUIDs at once and copy them all to your clipboard separated by newlines, which is useful for seeding databases, populating test fixtures, or pre-allocating identifiers.

Learn more

UUID Generator: Create Unique Identifiers Instantly

A UUID (Universally Unique Identifier) is a 128-bit value used to identify information in computer systems without requiring a central registration authority. UUID v4, the version generated by this tool, produces identifiers from cryptographically secure random numbers, making collisions statistically negligible even across distributed systems that never communicate with each other.

Understanding UUID v4 Structure

Every UUID v4 follows the canonical format xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx, where each x is a random hexadecimal digit. The 4 in the third group identifies the version, while the leading bits of y (constrained to 8, 9, a, or b) denote the variant as specified in RFC 9562. The remaining 122 bits are purely random, giving UUID v4 a keyspace of approximately 5.3 × 10^36 possible values.

Why Use UUID v4 Over Sequential IDs?

Auto-incrementing integer IDs are simple but introduce coupling: they require a single source of truth, leak information about record count and creation order, and create merge conflicts when combining databases. UUID v4 eliminates these issues. Any node — a browser, a microservice, a mobile app — can independently generate an identifier that is guaranteed to be unique for practical purposes. This property makes UUIDs essential in distributed architectures, event-driven systems, and offline-first applications.

Performance Considerations

UUID v4 values are not sequential, which can degrade index performance in B-tree-based databases such as PostgreSQL and MySQL InnoDB. Insertions become random rather than append-only, increasing page splits and write amplification. Mitigation strategies include UUID v7 (which embeds a timestamp prefix for monotonic ordering), ULID, or storing UUIDs as 16-byte binary columns instead of 36-char strings. For read-heavy workloads or small-to-medium tables, UUID v4 remains perfectly efficient.

Common UUID Use Cases

UUIDs serve as primary keys in relational and NoSQL databases, correlation IDs in distributed tracing (OpenTelemetry, Jaeger), idempotency keys for payment APIs (Stripe, PayPal), session tokens, file names for uploaded assets, and resource identifiers in RESTful APIs. Any scenario that demands globally unique, decentralized identification benefits from UUID v4.

Browser-Based Generation with the Web Crypto API

This tool uses crypto.randomUUID(), part of the Web Crypto API available in all modern browsers and Node.js 19+. The underlying entropy comes from the operating system's CSPRNG (e.g., /dev/urandom on Linux, BCryptGenRandom on Windows), ensuring output that is indistinguishable from true randomness for all practical applications. Unlike Math.random()-based UUID libraries, this approach is cryptographically secure and compliant with RFC 9562.

UUID Formats and Encoding

The standard string representation is 36 characters (32 hex digits plus 4 hyphens). For storage efficiency, UUIDs can be encoded as 16-byte binary (BINARY(16) in MySQL, uuid type in PostgreSQL), Base64 (22 characters), or Base62 (22 characters, URL-safe). When transmitting UUIDs in JSON APIs, the canonical lowercase hyphenated string is the de facto standard. This generator outputs both lowercase and uppercase formats to accommodate systems with different conventions.

UUID v4 vs. Other UUID Versions

UUID v1 embeds a MAC address and timestamp, providing natural ordering but exposing hardware identity. UUID v3 and v5 are deterministic, derived from a namespace and name via MD5 or SHA-1 hashing — useful for reproducible IDs but not random. UUID v7, defined in RFC 9562, combines a Unix timestamp with random bits for time-ordered uniqueness, offering the best of both worlds for database indexing. UUID v4 remains the most widely adopted version when ordering is not required and simplicity is preferred.