Content-Type
FormatDefinition
The Content-Type HTTP header indicates the media type of the resource. For request bodies, it tells the server how to parse the payload. For responses, it tells the browser how to render the content. Content-Type is one of the most important HTTP headers.
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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.