uniqid generator

Uniqid is a unique identifier generator originally derived from PHP's built-in uniqid() function, ported to JavaScript and other languages for environments where a simple, time-based identifier is needed without the overhead of a full UUID library. The PHP uniqid() function has been part of the language since PHP 4 and generates a string based on the current time in microseconds, optionally prepended with a prefix. The JavaScript port replicates this behavior, producing hexadecimal strings that reflect the generation timestamp with microsecond granularity. While uniqid is straightforward to use and produces short, readable identifiers, it was never designed for cryptographic security, distributed uniqueness, or high-concurrency environments. It is best understood as a legacy utility for simple, single-machine scenarios where a quick, non-repeating string is sufficient.

The original motivation behind PHP's uniqid() was pragmatic: web applications in the early 2000s needed a fast way to generate temporary filenames, form tokens, and session-adjacent identifiers without pulling in external libraries. The function served this role well for single-server PHP deployments, but its reliance on system time as the sole source of uniqueness became a liability as applications scaled. The JavaScript port carries the same fundamental limitation. Uniqid identifiers are not suitable for use as database primary keys in distributed systems, security tokens, or any context where globally guaranteed uniqueness is required.

How Uniqid Works

Uniqid generates identifiers by reading the current system time with microsecond precision and encoding it as a hexadecimal string. The generation process is straightforward: the function captures the Unix timestamp, splits it into seconds and microseconds, and concatenates the two values after converting each to its hexadecimal representation.

In PHP, the core uniqid() function produces a 13-character hex string by default. The first 8 characters encode the Unix timestamp in seconds, and the remaining 5 characters encode the microseconds. When the optional more_entropy parameter is set to true, PHP appends additional pseudo-random digits generated by a linear congruential generator (LCG), extending the output to 23 characters. The JavaScript port follows the same pattern, reading high-resolution time from the runtime environment and encoding it as hex.

The critical detail is that uniqid contains no randomness in its default mode. Two calls made at the exact same microsecond on the same machine will produce identical output. Even with the more_entropy flag enabled, the additional digits come from a weak pseudo-random source, not a cryptographically secure one. This means that uniqid values are predictable if an attacker knows the approximate generation time, and they offer no protection against enumeration attacks.

The encoding is plain hexadecimal with no version bits, variant markers, or structural metadata. There is no embedded machine identifier or process identifier, so two different servers generating uniqid values at the same microsecond will produce identical strings. The total entropy of a default uniqid is effectively zero beyond the time component, and even with the entropy flag, the additional randomness is on the order of 10^8 possible values, which is far below the collision resistance offered by modern identifier formats.

Because the timestamp occupies the leading characters, uniqid values do sort in approximate chronological order. However, the hex encoding of seconds and microseconds as separate segments means that the sort order is only correct within the same second; across second boundaries, the behavior depends on the exact hex values and is generally chronological but not guaranteed to be strictly lexicographic.

Use Cases

Temporary file naming on a single server. Uniqid remains a reasonable choice for generating temporary filenames on a single machine where the only requirement is that two files created in sequence do not collide. The microsecond precision is sufficient to prevent conflicts under normal load, and the short hex string integrates easily into file paths without escaping.

Legacy PHP application maintenance. Many existing PHP applications use uniqid() throughout their codebases for tasks such as generating cache keys, form nonces, or session-adjacent tokens. When porting these applications to Node.js or maintaining them in their original form, the uniqid library provides a drop-in replacement that preserves existing behavior. Rewriting all identifier generation to use a modern library may not be cost-effective for applications that are in maintenance mode.

Low-stakes deduplication tokens. In workflows where duplicate submissions are a nuisance rather than a security risk, uniqid can serve as a lightweight idempotency token. A form submission tagged with a uniqid value can be checked against recent submissions to prevent accidental double-posts. The token does not need to be globally unique or unpredictable because the threat model is user error, not adversarial manipulation.

Development and prototyping. During early development, teams sometimes need a quick identifier generator with zero configuration. Uniqid fills this role: it requires no initialization, produces a readable string, and works without external dependencies. As the application matures and moves toward production, the team should replace uniqid with a more robust format, but for prototyping it can reduce friction.

Comparison with Alternatives

Compared to Nano ID, uniqid is fundamentally weaker in every dimension that matters for production use. Nano ID generates identifiers using a cryptographically secure random number generator, provides configurable length and alphabet, and offers collision resistance that scales predictably with ID length. Uniqid offers none of these properties. Nano ID is the better choice for any scenario that requires unpredictable, collision-resistant identifiers, including URL slugs, API keys, and user-facing tokens. The only advantage uniqid holds is that it embeds a timestamp, which Nano ID does not.

When compared to UUID version 4, uniqid produces shorter strings but with drastically lower uniqueness guarantees. A UUID v4 has 122 bits of cryptographic randomness, making collisions effectively impossible across any practical scale. Uniqid's uniqueness depends entirely on time, and duplicate values are trivially produced by concurrent calls on multiple machines. For database primary keys, distributed systems, or any context where collisions carry real consequences, UUID v4 is the appropriate choice.

CUID2 represents the modern approach to collision-resistant identifiers. It uses a secure hash-based algorithm to produce identifiers that are both unpredictable and resistant to collision across distributed generators. CUID2 also avoids leaking timestamp information, which is a privacy benefit that uniqid cannot match. For new applications that need a compact, secure identifier without the overhead of full UUID infrastructure, CUID2 is a significantly better option than uniqid.

In summary, uniqid occupies a narrow niche: legacy compatibility and throwaway identifiers on single machines. For any modern application with meaningful uniqueness, security, or distribution requirements, one of the alternatives listed above should be preferred.