Query String
FormatDefinition
A query string is the part of a URL after the ? character, containing key-value pairs separated by & (e.g., ?page=2&sort=date). Query strings pass parameters to web servers and are commonly used for search filters, pagination, tracking, and API parameters.
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Regular Expression
A regular expression (regex) is a sequence of characters defining a search pattern. Regex is used for string matching, validation, extraction, and substitution in virtually all programming languages. Despite complex syntax, regex is an essential tool for text processing.
Cron Expression
A cron expression is a string of 5-6 fields defining a recurring schedule for automated tasks. Cron is the Unix job scheduler; cron expressions are also used in cloud functions, CI/CD pipelines (GitHub Actions), and backend frameworks to schedule periodic jobs.
UUID
A UUID (Universally Unique Identifier) is a 128-bit identifier formatted as 32 hex digits in 5 groups (xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx). UUIDs are designed to be unique across all systems without central coordination. UUID v4 is random; UUID v7 is time-sortable.
ULID
ULID (Universally Unique Lexicographically Sortable Identifier) is a 128-bit identifier that combines a 48-bit timestamp with 80 bits of randomness. ULIDs are URL-safe, case-insensitive, and lexicographically sortable — solving UUID v4's random ordering problem for database indexes.