Quick recommendation: For the safest, standards-based choice, use
GUID / UUID v4 (fully random) or
GUID / UUID v7 (time-ordered for databases). For specialized use cases, consider the alternatives below based on your specific requirements.
Overview
When choosing an identifier for your application or database schema, you have several options beyond standard GUIDs / UUIDs (governed by RFC 9562). Each format offers different trade-offs in terms of size, sortability, encoding and ecosystem support.
Comprehensive comparison table
| Feature | GUID/UUID v4 | GUID/UUID v7 | ULID | KSUID | Snowflake ID | NanoID | Cuid2 | XID |
|---|
| Size | 128-bit (16 bytes) | 128-bit (16 bytes) | 128-bit (16 bytes) | 160-bit (20 bytes) | 64-bit (8 bytes) | Variable (default 21 chars, ~126 bits) | Variable (default 24 chars, ~144 bits) | 96-bit (12 bytes) |
|---|
| Encoding | Hex with hyphens
36 chars | Hex with hyphens
36 chars | Base32
26 chars | Base62
27 chars | Decimal or Hex
19 digits | URL-safe Base64
21 chars default | Base36
24 chars default | Base32-like
20 chars |
|---|
| Time-sortable | No | Yes
Millisecond | Yes
Millisecond | Yes
Second | Yes
Millisecond | No
Fully random | Yes
Millisecond | Yes
Second |
|---|
| Standard | RFC 9562 | RFC 9562 | Community spec | Segment.io spec | Twitter/X spec | Library-specific | Community spec | Library-specific |
|---|
| Human-readable | Moderate
Hex with hyphens | Moderate
Hex with hyphens | Good
Base32, case-insensitive | Good
Base62, compact | Good
Short decimal | Excellent
URL-safe, compact | Good
Base36 | Moderate
Base32-like |
|---|
| Database-friendly | Good
Native UUID support, but random | Excellent
Native support + sortable | Good
Often stored as text/binary | Moderate
Larger storage | Excellent
Compact, native bigint | Moderate
Variable length | Moderate
Stored as text | Good
Compact, sortable |
|---|
| Collision resistant | Excellent
122 bits random | Excellent
74 bits random | Excellent
80 bits random | Excellent
128 bits random | Good
Depends on config | Excellent
Configurable entropy | Very Good
Multiple entropy sources | Very Good
52 bits random |
|---|
| Best for | General-purpose IDs, maximum compatibility, privacy-friendly | Database primary keys, event ordering, distributed systems | Human-friendly sortable IDs, URL-safe identifiers | Log/event systems, large-scale distributed tracing | High-throughput systems, Twitter-like platforms, sharded DBs | Short URLs, tokens, compact client-side IDs | Horizontal scaling, distributed systems, client-generated IDs | Compact IDs, MongoDB-like systems, Go applications |
|---|
Detailed comparison
Structure: 128 bits with 122 bits of randomness. No timestamp information.
- Pros: Universally supported, RFC standard, no time leakage, simple generation, native database support
- Cons: Random insertion pattern can cause index fragmentation in B-tree databases
- Use when: You want maximum compatibility and don't need time-ordering
Example: 550e8400-e29b-41d4-a716-446655440000
Structure: 128 bits with 48-bit Unix millisecond timestamp prefix + 74 bits randomness.
- Pros: RFC standard, time-ordered, database-friendly, widely supported, reduces index fragmentation
- Cons: Reveals creation timestamp (millisecond precision)
- Use when: You want time-ordering with RFC compliance for database primary keys
Example: 018f3f5e-1c2d-7a9b-8f10-3c4d5e6f7a8b
Structure: 128 bits with 48-bit Unix millisecond timestamp + 80 bits randomness, encoded in Base32.
- Pros: Compact representation (26 chars), case-insensitive, time-ordered, URL-safe, human friendly
- Cons: Not RFC GUID / UUID standard, requires library support, less universal than GUID / UUID
- Use when: You need human-friendly, sortable IDs and your stack supports ULID
Example: 01ARZ3NDEKTSV4RRFFQ69G5FAV
Structure: 160 bits with 32-bit Unix second timestamp + 128 bits randomness, encoded in Base62.
- Pros: Larger identifier space (160 bits), second-precision timestamp, k-sortable, very high entropy
- Cons: Not RFC standard, larger storage than UUID (20 vs 16 bytes), requires library support
- Use when: You need very large ID space for high-volume log/event systems
Example: 0o5Fs0EELR0fUjHjbCnEtdUwQe3
Structure: 64 bits with timestamp (41 bits) + machine/datacenter ID (10 bits) + sequence (12 bits).
- Pros: Very compact (8 bytes), time-ordered, high throughput, works well with sharding, native bigint support
- Cons: Requires coordination for machine IDs, limited to ~70 years from epoch, smaller ID space than 128-bit
- Use when: You need high-throughput ID generation in distributed systems with coordinated machine IDs
Example: 1142974645030174720
NanoID
Structure: Variable length (default 21 characters), URL-safe Base64 alphabet, fully random.
- Pros: Very compact, URL-safe, customizable length and alphabet, excellent for short URLs and tokens
- Cons: Not time-sortable, variable length can complicate database schemas, no standard
- Use when: You need compact, URL-safe IDs for client-side generation or short URLs
Example: V1StGXR8_Z5jdHi6B-myT
Cuid (Collision-resistant Unique Identifier)
Structure: ~200 bits with timestamp prefix + counter + fingerprint + random data, encoded in Base36.
- Pros: Optimized for horizontal scaling, client-generated, collision-resistant, sortable by time
- Cons: Larger than most alternatives (25 chars), requires library support, not widely adopted
- Use when: You need client-generated IDs in distributed systems with horizontal scaling
Example: cjld2cjxh0000qzrmn831i7rn
XID
Structure: 96 bits with timestamp (4 bytes) + machine ID (3 bytes) + process ID (2 bytes) + counter (3 bytes).
- Pros: Compact (12 bytes), time-sortable, similar to MongoDB ObjectID, works well with Go
- Cons: Smaller ID space than 128-bit formats, reveals machine information, Go-ecosystem focused
- Use when: You need MongoDB-like IDs in Go applications or compact time-sortable identifiers
Example: 9m4e2mr0ui3e8a215n4g
Which one should you use?
- Choose GUID / UUID v4 if you want the safest default: widely supported, easy to store, no embedded metadata, and simple generation.
- Choose GUID / UUID v7 if you want a standards-based ID that is time-ordered and typically behaves better as a database primary key than random GUIDs / UUIDs.
- Choose ULID if you want time-sortable IDs with a compact, human-friendly Base32 string representation, and your stack supports it.
- Choose KSUID if you need a larger ID space (160 bits) for very high-volume systems like logging or event tracking.
- Choose SnowflakeID if you need high-throughput ID generation in a distributed system with coordinated machine IDs and can work within a 64-bit space.
- Choose NanoID if you need compact, URL-safe IDs for short URLs, tokens, or client-side generation.
- Choose Cuid if you need client-generated IDs optimized for horizontal scaling and collision resistance.
- Choose XID if you're working in a Go ecosystem or need compact MongoDB-like IDs with time-sorting.
Practical guidance for databases
If your main concern is database performance and index locality, you usually want identifiers that don't insert randomly across the index.
- Most compatible: GUID / UUID v4 (works everywhere, but can be random for indexes)
- Best "standard + sortable" combo: GUID / UUID v7 (time-ordered while staying a real GUID / UUID)
- Best for high throughput: SnowflakeID (compact, fast generation, designed for distributed systems)
- Best for storage efficiency: SnowflakeID (8 bytes) or XID (12 bytes) for smaller footprint
- Non-standard but popular: ULID (sortable, human-friendly, requires library support)
Performance considerations
- B-tree indexes: Time-ordered IDs (v7, ULID, KSUID, SnowflakeID, XID) reduce page splits and improve insert performance in databases using B-tree indexes (PostgreSQL, MySQL, etc.).
- LSM-tree databases: Random IDs (v4, NanoID) may perform better in some LSM-tree databases (Cassandra, ScyllaDB), but this depends on partitioning strategy.
- Storage overhead: SnowflakeID (8 bytes) and XID (12 bytes) are more compact than 128-bit formats (16 bytes). Consider this for very large tables.
- Index size: Smaller IDs (SnowflakeID, XID) result in smaller indexes, which can improve cache utilization and query performance.
Interoperability and ecosystem support
GUID / UUID has the broadest support across programming languages, databases, and frameworks:
- Databases: Native GUID / UUID types in PostgreSQL, MySQL, SQL Server, Oracle, etc.
- Languages: Built-in support in Java, C#, Python, Go, Ruby, JavaScript and many more
- APIs: JSON, REST, GraphQL commonly use GUID / UUID for resource identifiers
- ORMs: Entity Framework, Hibernate, Django ORM and many others natively handle GUIDs / UUIDs
Most non-standard formats require third-party libraries for generation, parsing, and custom converters for ORMs and serialization frameworks.
Use case recommendations
| Use Case | Best Choice | Alternative |
|---|
| Database primary keys (general) | GUID/UUID v7 | ULID, SnowflakeID |
| High-throughput distributed systems | SnowflakeID | GUID/UUID v7, XID |
| REST API resource identifiers | GUID/UUID v4 or v7 | ULID, NanoID |
| Short URLs and tokens | NanoID | Cuid |
| Event logging and tracing | GUID/UUID v7 | KSUID, ULID |
| Client-side generation | GUID/UUID v4 | NanoID, Cuid |
| Microservices correlation IDs | GUID/UUID v7 | ULID, XID |
| MongoDB-style documents | XID | GUID/UUID v7 |
| Legacy system integration | GUID/UUID v4 | GUID/UUID v7 |
| Maximum compatibility | GUID/UUID v4 | GUID/UUID v7 |
Warnings and trade-offs
- Identifiers are not secrets: None of these ID formats should be used as security tokens or authentication secrets. They are identifiers, not cryptographic keys.
- Sorting depends on representation: "time-sortable" usually means the string form sorts by time, but database storage/byte-order can change behavior (varies by database/driver).
- Non-standard formats: ULID, KSUID, SnowflakeID, NanoID, Cuid and XID are not RFC standards. Some APIs, ORMs and databases assume GUID / UUID formatting and won't accept them without custom handling.
- Time leakage: Time-ordered IDs (v7, ULID, KSUID, SnowflakeID, XID) reveal approximate creation time. If that matters, prefer GUID / UUID v4 or NanoID.
- Interoperability matters: If you work across many systems or languages, GUIDs / UUIDs typically win due to universal support.
- Migration complexity: Switching from one identifier format to another in an existing system can be challenging and may require data migration.
- Machine coordination: SnowflakeID and XID require machine/process IDs, which adds operational complexity in containerized or serverless environments.
- Variable length concerns: NanoID and Cuid use variable or non-standard lengths, which can complicate database schema design and indexing.
Frequently Asked Questions
For most databases,
GUID / UUID v7 is the best choice. It combines RFC standardization with time-ordering, reducing index fragmentation. For very high-throughput systems, consider
SnowflakeID due to its compact size (8 bytes) and excellent performance characteristics.
No. Each format has its own structure, encoding, and size. You cannot convert between them without losing semantic information. While some are 128 bits (UUID, ULID), they encode timestamps and random data differently. Choose one format and stick with it throughout your system.
NanoID is the most compact and URL-safe option, with a default length of 21 characters. It's specifically designed for use in URLs, tokens, and places where compactness matters. ULID (26 chars) is another good choice if you need time-sorting as well.
Possible with conversion. Since ULID is 128 bits, you can convert it to a UUID binary representation and store it in PostgreSQL's
uuid type, but you'll lose the Base32 string representation. You may need to store ULID as
text or
bytea to preserve the original encoding. For native PostgreSQL support, use standard
UUIDs.
NanoID and ULID are the most human-readable due to their compact, URL-safe encodings. ULID uses Base32 (all uppercase, case-insensitive): 01ARZ3NDEKTSV4RRFFQ69G5FAV. NanoID uses URL-safe Base64: V1StGXR8_Z5jdHi6B-myT. Both are easier to read and copy than hex-based GUIDs/UUIDs.
All formats have extremely low collision risk when properly implemented. GUID/UUID v4 (122 bits random), ULID (80 bits/ms), KSUID (128 bits random), and others provide sufficient entropy. However, ensure your random number generator is cryptographically secure. Poor implementations or system clock issues (for time-based IDs) can increase risk.
XID is very similar to MongoDB's ObjectID (both 96-bit with timestamp, machine ID, process ID, and counter). If you're using MongoDB, stick with ObjectID. If you need a MongoDB-like ID outside of MongoDB (especially in Go), XID is a good choice. For broader compatibility, use
GUID/UUID v7.
GUID / UUID v7 is excellent for microservices. It provides time-ordering (useful for tracing and debugging), RFC compliance (works with standard libraries) and decentralized generation (no coordination needed). For extremely high-throughput services, consider
SnowflakeID.
Only if necessary. Migration is complex and risky. If your current ID system works well, there's usually no compelling reason to migrate. Consider migration only if you face specific performance issues (e.g., severe index fragmentation with random UUIDs) or need features your current format lacks. New projects should choose the right format from the start.
No. None of these formats are designed for security purposes. While they're hard to guess, they're not cryptographically secure tokens. For security tokens, API keys, or session IDs, use proper cryptographic methods (e.g., random bytes from a CSPRNG, signed JWTs, etc.).
GUID/UUID has the best library support across all languages and platforms. It's built into most standard libraries. SnowflakeID and ULID have good third-party library support in major languages. NanoID has excellent JavaScript/TypeScript support but is limited elsewhere. Others like KSUID, Cuid, and XID have more limited ecosystems.
Conclusion
For broad interoperability and standards compliance, choose a standard GUID / UUID: v4 for general-purpose fully random IDs or v7 for time-ordered database-friendly identifiers.
For specialized use cases:
- ULID: Human-friendly, time-sortable IDs with Base32 encoding
- SnowflakeID: High-throughput distributed systems with compact storage
- KSUID: Large-scale logging and event tracking systems
- NanoID: Compact URLs, tokens, and client-side generation
- Cuid: Client-generated IDs for horizontal scaling
- XID: Go applications needing MongoDB-like compact IDs
Remember that choosing an identifier format is a long-term architectural decision. Consider your requirements for standardization, ecosystem support, performance and interoperability before committing to a format.