Question 1

I get an "invalid percent-encoding" error — what does that mean?

Accepted Answer

It means your input has a % that is not followed by exactly two valid hexadecimal digits — for example a trailing % at the end of the string, or %2 with only one digit. That is a malformed escape sequence and cannot be decoded unambiguously, so the tool reports it rather than guessing.

Question 2

Does decoding turn a + back into a space?

Accepted Answer

No — this decodes strict percent-encoding (decodeURIComponent), which treats + as a literal plus character, not a space. The +-means-space convention belongs to application/x-www-form-urlencoded (HTML form submissions), a related but different format. If you're decoding a form-encoded query string where + represents spaces, replace + with %20 before pasting it here.

Question 3

What happens if I paste text that has no percent-encoding in it at all?

Accepted Answer

It passes through unchanged — decoding a string with no %XX sequences is a no-op, so it's safe to paste text you're not sure is encoded and see if anything changes.

URL Decode

Standards Compliant

Clear Error Messages

Handles Large Text

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