Free ULID Generator & Decoder

Generate universally unique, lexicographically sortable identifiers instantly. Decode existing ULIDs to extract timestamps and understand their structure.

ULID Generator & Decoder

Generate unique, sortable identifiers or decode existing ULIDs to extract timestamps

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What is a ULID?

A ULID (Universally Unique Lexicographically Sortable Identifier) is a 128-bit identifier that combines a timestamp with randomness to create unique, sortable IDs. Unlike UUIDs, ULIDs are designed to be both unique and chronologically sortable.

Each ULID consists of two parts: a 48-bit timestamp (milliseconds since Unix epoch) and an 80-bit random component. This means ULIDs generated within the same millisecond are still unique due to the random portion, while maintaining sort order based on creation time.

ULIDs are encoded using Crockford's Base32, which uses 26 characters (excluding I, L, O, U to avoid confusion) resulting in a 26-character string that's URL-safe, case-insensitive, and human-readable.

ULID Generator Features

Embedded Timestamp

Every ULID contains a precise millisecond timestamp that can be extracted without additional database columns.

Lexicographically Sortable

ULIDs sort naturally in chronological order, making them perfect for time-series data and event logs.

Cryptographically Random

The random component uses secure random number generation to ensure uniqueness even within the same millisecond.

Instant Decoding

Extract timestamps and validate ULIDs instantly in your browser - no server required, completely private.

Database Optimized

Better index performance than UUIDs due to sequential ordering, reducing page splits and fragmentation.

URL & Case Safe

Uses Crockford's Base32 encoding - no special characters, case-insensitive, and safe for URLs and filenames.

How to Use the ULID Generator & Decoder

1Generating ULIDs

  1. Step 1: Select the "Generate" tab in the tool above.
  2. Step 2: Choose how many ULIDs to generate (1 to 1,000).
  3. Step 3: Optionally set a custom timestamp for the ULIDs.
  4. Step 4: Click "Generate ULID" to create your identifiers.
  5. Step 5: Copy individual ULIDs or download all as a text file.

2Decoding ULIDs

  1. Step 1: Select the "Decode" tab in the tool above.
  2. Step 2: Paste or type the ULID you want to decode.
  3. Step 3: Click "Decode ULID" to extract the information.
  4. Step 4: View the extracted timestamp in multiple formats.
  5. Step 5: See the ULID structure breakdown (timestamp vs random parts).

Understanding ULID Structure

01ARZ3NDEK
TSV4RRFFQ69G5FAV
Timestamp (10 chars)
Random (16 chars)

Timestamp Component

  • • 48-bit Unix timestamp in milliseconds
  • • Encodes to 10 Base32 characters
  • • Provides sortability by creation time
  • • Valid until year 10889

Random Component

  • • 80-bit cryptographically random value
  • • Encodes to 16 Base32 characters
  • • Ensures uniqueness within same millisecond
  • • ~1.21 quintillion possible values

Crockford's Base32 Alphabet

ULIDs use Crockford's Base32 encoding, which excludes easily confused characters:

0123456789ABCDEFGHJKMNPQRSTVWXYZ

Excluded: I (confused with 1), L (confused with 1), O (confused with 0), U (accidental obscenity)

Why Choose ULIDs Over UUIDs?

✅ ULID Advantages

  • • Lexicographically sortable by creation time
  • • Better database index performance
  • • Embedded timestamp (no extra column needed)
  • • More compact representation (26 vs 36 chars)
  • • Case-insensitive and URL-safe
  • • No special characters (hyphens)

📊 Best Use Cases

  • • Event logging and audit trails
  • • Distributed database primary keys
  • • Time-series data identification
  • • Message queue ordering
  • • Session and request tracking
  • • File and object naming

Frequently Asked Questions About ULIDs

ULID (Universally Unique Lexicographically Sortable Identifier) is a 128-bit identifier like UUID, but with key differences: ULIDs are sortable by creation time, contain an embedded timestamp, are more compact (26 vs 36 characters), use no hyphens, and are case-insensitive. This makes ULIDs ideal for distributed systems where chronological ordering matters.

Use our free online ULID generator above. Simply select how many ULIDs you need (up to 1,000), optionally set a custom timestamp, and click "Generate ULID". You can copy individual ULIDs or download all of them as a text file.

Switch to the "Decode" tab in our tool, paste your ULID, and click "Decode ULID". The tool will extract and display the embedded timestamp in multiple formats (Unix milliseconds, UTC, and local time), plus show you the ULID structure breakdown.

Yes, ULIDs are designed for uniqueness across distributed systems. The combination of millisecond timestamp and 80-bit random component (over 1.21 quintillion possibilities) makes collisions extremely unlikely. Even generating millions of ULIDs per second, you'd expect to wait billions of years for a collision.

Crockford's Base32 is an encoding scheme that uses 32 alphanumeric characters (0-9, A-Z) but excludes I, L, O, and U to avoid confusion with 1, 1, 0, and to prevent accidental obscenity. This makes ULIDs more readable and less error-prone when transcribed.

Absolutely! ULIDs are excellent for database primary keys. Their lexicographic sortability means sequential inserts maintain order, reducing B-tree index fragmentation compared to random UUIDs. The embedded timestamp also eliminates the need for a separate created_at column in many cases.

ULIDs use a 48-bit timestamp representing milliseconds since Unix epoch. This allows timestamps up to approximately 281 trillion milliseconds, or about the year 10889 AD. This is more than sufficient for any practical application.

No, ULIDs are case-insensitive. You can use uppercase or lowercase letters interchangeably. Our decoder normalizes input to uppercase automatically. This makes ULIDs easier to work with in case-insensitive systems like URLs or some database columns.

Theoretically, you can generate 2^80 (about 1.21 quintillion) unique ULIDs per millisecond due to the random component. Our tool can generate up to 1,000 ULIDs at once for practical use cases. For production systems, there's effectively no practical limit.

Yes, our ULID generator and decoder is completely free. There's no registration required, no usage limits, and all processing happens in your browser for privacy. You can generate and decode as many ULIDs as you need.

Yes! Our generator allows you to specify a custom timestamp using the date/time picker. This is useful for testing, creating backdated identifiers, or generating ULIDs for specific time periods.

ULID libraries exist for most popular languages including JavaScript/TypeScript, Python, Go, Rust, Java, C#, Ruby, PHP, and many more. The ULID specification is open and well-documented, making implementation straightforward.

Generate and decode ULIDs (Universally Unique Lexicographically Sortable Identifiers) instantly.

Tool
Free ULID Generator & Decoder Online
Category
All tools
Availability
Browser-based tool