# UUIDDev

> Free UUID generator and developer reference for UUID v4 and v7. All tools run entirely in the browser — no server, no logging. Content covers UUID standards (RFC 9562), version differences, database usage, security, and language-specific implementation guides.

## Tools

- [UUID Generator](https://www.uuiddev.com/): Generate UUID v7 or v4 instantly in the browser. RFC 9562-compliant, monotonic counter for v7.
- [UUID v7 Generator](https://www.uuiddev.com/uuid-v7): Time-sortable UUID v7 with per-millisecond monotonic counter. Default for database primary keys.
- [UUID v4 Generator](https://www.uuiddev.com/uuid-v4): Random UUID v4 from the Web Crypto API. Default for externally visible identifiers.

## Tools

- [UUID Validator](https://www.uuiddev.com/tools/uuid-validator): Check any UUID string — format, version digit, variant bits, RFC 9562 compliance. Accepts v1–v8, nil, max.
- [UUID Decoder](https://www.uuiddev.com/tools/uuid-decoder): Inspect a UUID — read version, variant, and for v1/v7 decode the embedded timestamp to a date.
- [UUID Converter](https://www.uuiddev.com/tools/uuid-converter): Convert UUID between standard string, 32-char hex, Base64, URL-safe Base64, URN, and 16-byte binary.
- [Tools Index](https://www.uuiddev.com/tools): All UUID tools in one place.

## Guides

- [What is a UUID?](https://www.uuiddev.com/what-is-a-uuid): UUID meaning, format, versions overview, use cases, and common mistakes.
- [UUID v4 vs UUID v7](https://www.uuiddev.com/uuid-v4-vs-v7): Bit layout differences, database index behaviour, timestamp disclosure risks, and migration path.
- [UUID Versions](https://www.uuiddev.com/guides/uuid-versions): All RFC 9562 versions (v1–v8) explained — what each does, which are deprecated, and when to use each.
- [UUID vs GUID](https://www.uuiddev.com/guides/uuid-vs-guid): GUID is Microsoft's name for UUID. Same standard, SQL Server byte-order caveat, .NET Guid type.
- [UUID vs ULID](https://www.uuiddev.com/guides/uuid-vs-ulid): 128-bit time-sortable identifiers compared — encoding, monotonicity, database support, ecosystem.
- [UUID in Databases](https://www.uuiddev.com/guides/uuid-in-databases): Storage types for PostgreSQL, MySQL, SQLite, MongoDB. v4 vs v7 index performance. Migration guide.
- [UUID Security](https://www.uuiddev.com/guides/uuid-security): What UUID v4 guarantees, what v7 leaks, and when to use a real secret instead of a UUID.
- [UUID in JavaScript](https://www.uuiddev.com/guides/uuid-in-javascript): crypto.randomUUID(), uuid npm package, React, Vue, Prisma, Drizzle, TypeScript patterns.
- [UUID in Python](https://www.uuiddev.com/guides/uuid-in-python): Built-in uuid module, v7 in Python 3.13+, uuid6 backport, Django, SQLAlchemy, Pydantic, FastAPI.
- [UUID in Go](https://www.uuiddev.com/guides/uuid-in-go): google/uuid package, v4 and v7 generation, pgx, database/sql, GORM, slog, typed UUID patterns.
- [Guides Index](https://www.uuiddev.com/guides): All UUID guides in one place.

## Glossary

- [UUID](https://www.uuiddev.com/glossary/uuid): Definition, format, versions, common uses, and what a UUID is not.
- [GUID](https://www.uuiddev.com/glossary/guid): GUID is Microsoft's name for UUID. Same standard, SQL Server byte-order quirk, .NET Guid.Empty.
- [UUID Variant](https://www.uuiddev.com/glossary/variant): The 2-bit field at position 17 identifying the UUID layout specification — 8, 9, a, or b for RFC 9562.
- [UUID Namespace](https://www.uuiddev.com/glossary/namespace): A UUID used as a scope for name-based generation (v3/v5). Standard namespaces for DNS, URL, OID, X.500.
- [UUID Collision](https://www.uuiddev.com/glossary/collision): Probability mathematics — why 2.7 × 10¹⁸ v4 UUIDs are needed before a collision becomes likely.
- [Nil UUID](https://www.uuiddev.com/glossary/nil-uuid): All-zeros UUID (00000000-0000-0000-0000-000000000000) — sentinel for absent/unset UUID values.
- [UUID Entropy](https://www.uuiddev.com/glossary/entropy): The 122 bits of CSPRNG randomness in v4 that make UUIDs unpredictable and collision-safe.
- [Lexicographical Order](https://www.uuiddev.com/glossary/lexicographical-order): Why UUID v7 sorts chronologically as a plain string — and why that matters for database index performance.
- [Glossary Index](https://www.uuiddev.com/glossary): All UUID terms defined in one place.

## Key facts

- All UUID generation is client-side. No values are transmitted to or stored by the server.
- UUID v7 is the recommended default for database primary keys in 2026 (RFC 9562, PostgreSQL 18 native support).
- UUID v4 is the recommended default for externally visible identifiers (URLs, tokens, share links).
- GUID and UUID are the same standard — GUID is the Microsoft term.
- The site implements RFC 9562 §6.2 Method 1 monotonic counter for v7.