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The UUID/ULID Generate/Decode tool creates universally unique identifiers using industry-standard UUID formats (v4, v7) and ULID (Universally Unique Lexicographically Sortable Identifier). It also decodes ULID values to extract their embedded timestamps.

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Use Cases

  • Database primary keys that need to be globally unique
  • Distributed system identifiers for microservices and APIs
  • Session IDs and authentication tokens
  • File naming for uploads or generated assets
  • Sortable IDs where chronological ordering matters (UUID v7, ULID)
  • Debugging to extract timestamps from ULID values

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UUID vs ULID

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UUID v4 (Random)

  • 128-bit random identifier
  • Format: 550e8400-e29b-41d4-a716-446655440000
  • Not sortable by creation time
  • Cryptographically random (uses Web Crypto API)

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UUID v7 (Time-based, Sortable)

  • 128-bit identifier with timestamp prefix
  • Format: 01890a5d-ac96-774b-bcce-b302099a8057
  • Sortable by creation time (timestamp in first 48 bits)
  • Combines Unix timestamp (ms) + random bits

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ULID (Universally Unique Lexicographically Sortable ID)

  • 128-bit identifier, 26-character Crockford Base32 encoding
  • Format: 01H2XCEJQTF2NBREXX3VQJHP41
  • Sortable by creation time (timestamp in first 10 characters)
  • URL-safe (no special characters, case-insensitive)
  • Monotonic: guarantees ordering even within the same millisecond
Use UUID v4 for maximum randomness when sortability doesn’t matter. Use UUID v7 or ULID when you need IDs that sort chronologically. ULID has the advantage of being shorter and URL-safe.

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Actions

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Generate (Default)

Generates one of each type: 
550e8400-e29b-41d4-a716-446655440000  (UUID v4)
01890a5d-ac96-774b-bcce-b302099a8057  (UUID v7)
01H2XCEJQTF2NBREXX3VQJHP41           (ULID)

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UUID v4

Generates a single random UUID v4: 
7c9e6679-7425-40de-944b-e07fc1f90ae7

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UUID v7

Generates a single timestamp-based UUID v7: 
01890a5d-ac96-774b-bcce-b302099a8057

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ULID

Generates a single ULID: 
01H2XCEJQTF2NBREXX3VQJHP41

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Decode ULID

Extracts the timestamp from a ULID: Input: 
01H2XCEJQTF2NBREXX3VQJHP41
Output: 
2024-03-04T10:23:45.678Z

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Output Format

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UUID Format

  • Length: 36 characters (32 hex digits + 4 hyphens)
  • Encoding: Hexadecimal (0-9, a-f)
  • Example: 01890a5d-ac96-774b-bcce-b302099a8057

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ULID Format

  • Length: 26 characters
  • Encoding: Crockford Base32 (0-9, A-Z excluding I, L, O, U)
  • Example: 01H2XCEJQTF2NBREXX3VQJHP41
  • Structure:
    • First 10 characters: Timestamp (48 bits, milliseconds since Unix epoch)
    • Last 16 characters: Randomness (80 bits)

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Examples

Action: Generate (default)

Output:
550e8400-e29b-41d4-a716-446655440000
01890a5d-ac96-774b-bcce-b302099a8057
01H2XCEJQTF2NBREXX3VQJHP41

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Technical Details

Located in lib/tools/engine.ts:472-481
The tool uses these libraries:
  • uuid package: Generates UUID v4 and v7 using Web Crypto API
  • ulidx package: Generates monotonic ULIDs and decodes timestamps

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ULID Monotonicity

The tool uses monotonicFactory() from ulidx to ensure that ULIDs generated in the same millisecond have incrementing values: 
import { monotonicFactory } from 'ulidx';
const ulidGen = monotonicFactory();
const id1 = ulidGen(); // 01H2XCEJQTF2NBREXX3VQJHP41
const id2 = ulidGen(); // 01H2XCEJQTF2NBREXX3VQJHP42 (increments if same ms)

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UUID v7 Timestamp Structure

UUID v7 embeds a Unix timestamp (milliseconds) in the first 48 bits: 
01890a5d-ac96-774b-bcce-b302099a8057
└──────┘
  ↑
Timestamp (48 bits)

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Randomness Source

Both UUID and ULID generation use cryptographically secure random number generators:
  • Browser: crypto.getRandomValues() (Web Crypto API)
  • Node.js: crypto.randomBytes() (Node.js crypto module)
ULID decoding only works for valid ULID strings. If you pass a UUID or malformed string to “Decode ULID”, you’ll get an error or incorrect timestamp.

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Comparison Table

FeatureUUID v4UUID v7ULID
Length36 chars36 chars26 chars
SortableNoYesYes
URL-safeNo (hyphens)No (hyphens)Yes
Case-sensitiveNoNoNo
TimestampNoYes (48-bit)Yes (48-bit)
Collision resistance2^1222^74 (per ms)2^80 (per ms)
EncodingHexHexBase32

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Common Patterns

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Database Primary Keys

CREATE TABLE users (
  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  -- or for sortable:
  id UUID PRIMARY KEY DEFAULT uuid_v7(),
  -- or ULID (stored as string):
  id VARCHAR(26) PRIMARY KEY
);

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REST API Identifiers

GET /api/users/01H2XCEJQTF2NBREXX3VQJHP41

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Sortable Log Entries

const logEntry = {
  id: ulid(), // Automatically sorts by creation time
  level: 'INFO',
  message: 'User logged in'
};

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