FormatURLs

FormatURLs is a generic utility concept used to transform one or more URL strings into standardized, display-friendly, and safe representations. It can be implemented as a function or library in many programming languages and is commonly used in web applications to render links, validate input, or compare URLs for deduplication.

Its core capabilities include normalization, validation, encoding, and display formatting. Normalization may trim whitespace, lower-case the host, remove default ports, and resolve relative paths. Validation checks syntax against standards such as RFC 3986. Encoding ensures reserved characters are percent-encoded and non-ASCII characters are handled via IDN punycode and percent-encoding where appropriate. Display formatting allows choosing a full URL, a shortened form that shows only the host, or a trimmed version that hides sensitive query parameters. Some implementations also collapse or reorder query parameters for comparison.

Security and safety considerations are central. Any output should be escaped in HTML contexts to prevent XSS. Sanitization may remove or rewrite dangerous components, such as javascript: schemes or redirects. When accepting user input, it is important to decide whether to preserve the original URL, or to normalize to a canonical form while maintaining the ability to reconstruct the original if needed.

Usage scenarios include rendering lists of links, logging and analytics, or de-duplicating URLs in datasets. It is important to understand that some transformations can alter semantics, especially around query strings and fragments, so the intended use determines which components to preserve or remove.

Common configurable options include maximum length, display mode, whether to preserve or strip the query, whether to normalize case, and whether to convert IDNs to punycode.