Turns %20 back into a space and %C3%A9 back into é. Most often used to read what an analytics URL, a redirect chain or a log line actually contains.
The plus-sign ambiguity
+ means a space in form-encoded data and a literal plus everywhere else, and nothing in the string tells you which applies. The default here treats it as a space, which is right for the query strings people usually paste.
Turn it off when the value is Base64 (where + is part of the alphabet and turning it into a space corrupts the data), a phone number in E.164 format, or anything mathematical.
Double encoding
%25 followed by two hex digits, the string was encoded twice — %25 is the escape for the percent sign itself. That happens whenever a value is encoded by application code and then again by a framework. Run it through the tool a second time.
The tell is %2520, which decodes to %20, which decodes to a space.
When decoding fails
% not followed by two hex digits is invalid, and you get its exact position. This normally means the string was truncated, or that a literal percent sign was never escaped as %25 in the first place — a genuine bug in whatever produced it.Other names for this
Also searched as “urldecode online”, “decode url”, “percent decode”.
Questions
- The output still has percent signs in it.
- It was encoded twice. Decode again —
%2520becomes%20becomes a space. - My Base64 value came out with spaces in it.
- Turn off “Treat + as a space”. Plus is part of the standard Base64 alphabet.
- Does my text leave the browser?
- No. Everything runs as JavaScript in this tab — there is no server involved and no request is made. Open the Network panel and watch, or turn your Wi-Fi off and keep using the tool.