🧾 The Ultimate UUID Cheat Sheet for 2025

UUIDs (Universally Unique Identifiers) are everywhere — from primary keys and session tokens to distributed object identifiers. This cheat sheet gives you the complete rundown on UUIDs, updated for 2025.

Use it to choose the right version, avoid common mistakes, and reference language-specific generation code.

🔢 UUID Versions Overview

Version	Description	Properties	Use Case
v1	Time + MAC address	Ordered, traceable	Legacy systems, internal indexing
v2	DCE Security	Rare, POSIX-specific	Obsolete
v3	MD5-hash namespace	Deterministic	Stable namespacing
v4	Random-based	Collision-resistant, fast	Default for most apps
v5	SHA-1 namespace	Deterministic, secure	Versioned naming
v6	Reordered v1	Deprecated in favor of v7	Time-ordered but not adopted
v7	Timestamp + randomness	Sortable, secure	Logging, analytics, ordering
v8	Custom layout	Flexible, experimental	Custom IDs with embedded data

🧪 Which UUID Version Should You Use?

v4: For general purpose IDs (users, sessions, etc.)
v7: For log/event ordering, Kafka, time-indexed stores
v5: For generating same ID from name + namespace (e.g. DNS)
v8: For internal IDs with custom fields (e.g. tenant, region)

⚙️ UUID Generation Techniques by Language

Go

import "github.com/google/uuid"

uuid.New()         // v4
uuid.NewMD5(...)   // v3
uuid.NewSHA1(...)  // v5

Python

python

import uuid

uuid.uuid4()        # Random
uuid.uuid1()        # Time + MAC
uuid.uuid3(uuid.NAMESPACE_DNS, "example.com")
uuid.uuid5(uuid.NAMESPACE_DNS, "example.com")

JavaScript (Node.js)

import { v4, v5 } from 'uuid';

v4(); // Random UUID
v5('example.com', v5.DNS); // Name-based

Rust

rust

use uuid::Uuid;

Uuid::new_v4();
Uuid::new_v5(&Uuid::NAMESPACE_DNS, b"example.com");

Bash / CLI

bash

uuidgen       # Default v4 or v1 (OS dependent)
uuid -v       # See version if supported

🔍 UUID Format & Encoding

Hex format: 550e8400-e29b-41d4-a716-446655440000
Bytes (binary): 16 bytes (128 bits)
Base36: Shorter, alphanumeric (for URLs)
Base58/Base62: Compact, URL-safe alternatives
Multibase (e.g., IPFS): Includes prefix for encoding type

Example: UUID in base58

bash

pip install base58
python -c "import uuid, base58; print(base58.b58encode(uuid.uuid4().bytes))"

🧠 UUID Design Best Practices

✅ DO:

Use UUIDv4 for simple, secure, random IDs
Use UUIDv7 when order matters (timestamps)
Use UUIDv5 when deriving IDs from names
Store UUIDs in binary (BINARY(16)) in MySQL/Postgres for performance
Index UUID columns properly (especially with non-sequential types)

❌ DON’T:

Don’t use UUIDv1 in public-facing contexts (leaks MAC, timestamp)
Don’t use UUIDs as primary index if write amplification matters (v4 causes fragmentation)
Don’t truncate UUIDs — you’ll lose uniqueness guarantee

⚖️ UUID Performance and Storage

Size: 128-bit = 16 bytes
MySQL/Postgres: Prefer UUID or BINARY(16) over VARCHAR(36)
MongoDB: Use BinData type
Redis: UUIDs used as string keys

Indexing Tips

Avoid using UUIDv4 as clustered primary key
Consider sequential-friendly formats (e.g., UUIDv7, KSUID, ULID)
Batch inserts to reduce random I/O

🔐 UUID Security Tips

UUIDs are not cryptographic tokens (unless generated securely)
Use UUIDv4 from a CSPRNG (not Math.random)
Don’t encode sensitive info (e.g., email, PII) in UUIDv8 without encryption
For signed/secure IDs, look at JWKs, JWTs, or DIDs

🔄 UUID Conversion Cheats

Hex → Base58

python

import uuid, base58
base58.b58encode(uuid.UUID("550e8400-e29b-41d4-a716-446655440000").bytes)

UUID → Int

python

int(uuid.uuid4())

📊 UUID Comparison Table

Feature	v1	v3/v5	v4	v7	v8
Ordered	✅	❌	❌	✅	✅*
Deterministic	❌	✅	❌	❌	✅*
Privacy-Safe	❌	✅	✅	✅	✅
Sortable	❌	❌	❌	✅	✅*
Custom Payload	❌	❌	❌	❌	✅
RFC Standard	✅	✅	✅	✅	✅

*UUIDv8 allows you to define all of the above yourself — just be careful.

🚀 UUID Alternatives to Know

ULID: Time-sorted + random (base32)
KSUID: Sortable, secure IDs with timestamp
Snowflake: Compact, sortable (used by Twitter, Discord)
CIDs: Content-addressable hashes (IPFS)
DIDs: Decentralized identity identifiers (W3C)

📚 Helpful Tools and Libraries

[uuidtools.com](https://www.uuidtools.com) – generate + inspect UUIDs
[uuid.online](https://uuid.online) – decode/encode viewer
uuid-cli, uuidgen – CLI utilities
hashids, shortuuid, base62 – alternatives for compact IDs

🧩 When Not to Use UUIDs

When you need incrementing values for analytics
When you can guarantee central coordination (e.g. Snowflake IDs)
When you need cryptographic integrity or traceability → use CIDs/DIDs

Final Thoughts

Whether you’re just generating IDs for new users or designing the next globally distributed database, choosing the right UUID version and implementation matters.

UUIDs are simple — but not trivial. Understanding their trade-offs in performance, storage, privacy, and interoperability will help you build more scalable and resilient systems.

Keep this cheat sheet bookmarked, and you’ll be the UUID wizard on your team 🧙‍♂️

The Ultimate UUID Cheat Sheet for 2025