URL encoding, also known as percent encoding, is a mechanism for encoding information in a Uniform Resource Identifier (URI). It converts characters that are not allowed in a URL into a % followed by two hexadecimal digits representing the character's byte value in UTF-8. For example, a space becomes %20, and the Chinese character "你" becomes %E4%BD%A0. This ensures URLs remain valid and can be transmitted reliably over the internet.

encodeURI is designed to encode an entire URL, preserving characters that have syntactic meaning in a URI: : / ? # @ & = + $ , ; are left unencoded. It's suitable for encoding a complete URL string.

encodeURIComponent encodes all characters except: A-Z a-z 0-9 - _ . ! ~ * ' ( ). This makes it ideal for encoding individual query parameter values, path segments, or any data that should be treated as a literal string within a URL. Use encodeURIComponent when building query strings programmatically.

The application/x-www-form-urlencoded format (used by HTML forms) encodes spaces as + signs instead of %20. If you're encoding data for a traditional form submission (GET or POST with default enctype), enable this option. For modern REST APIs and general URL encoding, keep it off to use %20 for spaces, which is the standard percent-encoding approach.

Yes! Modern URL encoding uses UTF-8 as the character encoding. Emoji like 😀 (U+1F600) are encoded as their UTF-8 byte sequence: %F0%9F%98%80. Characters from any language—Chinese, Arabic, Cyrillic, etc.—are all properly handled. This tool uses JavaScript's built-in encodeURIComponent which operates on UTF-8, ensuring full Unicode support.

When enabled, each line of your input is encoded or decoded independently. This is particularly useful when you have a list of values that need individual encoding (e.g., multiple parameter values, a list of URLs, or batch processing). Without this mode, the entire text block—including newline characters—is encoded as a single string, and newlines become %0A.

Common reasons include: (1) The input contains invalid percent sequences like a lone % not followed by two hex digits—this throws a URIError. (2) The data was encoded with a different character encoding (e.g., legacy GBK instead of UTF-8), causing mojibake. (3) Double encoding—text that was encoded twice (e.g., %25 instead of %). Try decoding once and check if the result looks like it still contains percent signs; if so, decode again.

According to RFC 3986, unreserved characters that are always safe in a URL include: uppercase and lowercase letters (A-Z a-z), digits (0-9), and four special characters: - _ . ~. All other characters—including spaces, punctuation, non-ASCII characters, and reserved characters like : / ? # [ ] @ ! $ & ' ( ) * + , ; =—must be percent-encoded when used as data within a URL component.

Proper URL encoding is critical for SEO-friendly URLs. Clean, correctly encoded URLs ensure search engines can crawl and index your pages without issues. Use this tool to: validate that dynamic URLs with user-generated content are properly encoded; ensure internationalized URLs work correctly; debug redirect chains involving encoded parameters; and build safe query strings for API calls. The URL parser also helps you inspect and understand complex URLs at a glance.