Question 1

When do I need to decode a URL?

Accepted Answer

You need to decode URLs when reading server logs with percent-encoded query strings, debugging API responses that contain encoded parameters, parsing redirect URLs in OAuth flows, or making sense of URLs copied from browser address bars that contain encoded characters.

Question 2

What do %20 and %2F mean?

Accepted Answer

%20 represents a space character (ASCII 32 = hex 20). %2F represents a forward slash (/). In general, percent-encoded sequences like %XX represent the byte with hexadecimal value XX in the UTF-8 encoding of the original character.

Question 3

What is the difference between decodeURI and decodeURIComponent?

Accepted Answer

decodeURIComponent decodes all percent-encoded sequences including those representing URL structural characters like %2F (/), %3F (?), and %26 (&). decodeURI leaves those structural sequences intact and only decodes sequences that represent non-URL characters, preserving the URL structure.

Question 4

What happens when I try to decode malformed percent sequences?

Accepted Answer

Malformed percent sequences like %GG (non-hex digits) or %2 (incomplete sequence) cause a URIError in JavaScript. This tool catches the error and shows an error message. If possible it will try the alternative decode function as a fallback before reporting failure.

Question 5

How do I handle double-encoded URLs?

Accepted Answer

A double-encoded URL has sequences like %2520 instead of %20. To fully decode it, apply decoding twice. Run the decoder once to get %20, then run it again to get a space. Some systems double-encode parameters accidentally; this is a common source of bugs.

Question 6

How can URL decoding help with web traffic debugging?

Accepted Answer

Server access logs often store URLs in percent-encoded form. Decoding them makes query parameters, search terms, and path segments human-readable, helping you identify which pages users visited and what they searched for.

Question 7

How are Korean characters decoded from a URL?

Accepted Answer

Korean characters are encoded as their UTF-8 byte sequences in percent format. For example %EC%95%88%EB%85%95 decodes to 안녕 because EC 95 88 is the UTF-8 encoding of 안 and EB 85 95 is the encoding of 녕.

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