Sometimes the spaces get URL encoded to the + sign, some other times to %20. What is the difference and why should this happen?
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urlencode
http://www.example.com/some/path/to/resource?param1=value1
The part before the question mark must use % encoding (so %20 for space), after the question mark you can use either %20 or + for a space. If you need an actual + after the question mark use %2B.
Its better to always encode spaces as %20, not as "+".
It was RFC-1866 (HTML 2.0 specification), which specified that space characters should be encoded as "+" in "application/x-www-form-urlencoded" content-type key-value pairs. (see paragraph 8.2.1. subparagraph 1.). This way of encoding form data is also given in later HTML specifications, look for relevant paragraphs about application/x-www-form-urlencoded.
Here is an example of such a string in URL where RFC-1866 allows encoding spaces as pluses: "http://example.com/over/there?name=foo+bar". So, only after "?", spaces can be replaced by pluses, according to RFC-1866. In other cases, spaces should be encoded to %20. But since it's hard to determine the context, it's the best practice to never encode spaces as "+".
I would recommend to percent-encode all character except "unreserved" defined in RFC-3986, p.2.3
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
What's the difference: See other answers.
When use + instead of %20? Use + if, for some reason, you want to make the URL query string (?.....) or hash fragment (#....) more readable. Example: You can actually read this:
https://www.google.se/#q=google+doesn%27t+encode+:+and+uses+%2B+instead+of+spaces
(%2B = +)
But the following is a lot harder to read: (at least to me)
I would think + is unlikely to break anything, since Google uses + (see the 1st link above) and they've probably thought about this. I'm going to use + myself just because readable + Google thinks it's OK.
So, the answers here are all a bit incomplete. The use of a '%20' to encode a space in URLs is explicitly defined in RFC3986, which defines how a URI is built. There is no mention in this specification of using a '+' for encoding spaces - if you go solely by this specification, a space must be encoded as '%20'.
The mention of using '+' for encoding spaces comes from the various incarnations of the HTML specification - specifically in the section describing content type 'application/x-www-form-urlencoded'. This is used for posting form data.
Now, the HTML 2.0 Specification (RFC1866) explicitly said, in section 8.2.2, that the Query part of a GET request's URL string should be encoded as 'application/x-www-form-urlencoded'. This, in theory, suggests that it's legal to use a '+' in the URL in the query string (after the '?').
But... does it really? Remember, HTML is itself a content specification, and URLs with query strings can be used with content other than HTML. Further, while the later versions of the HTML spec continue to define '+' as legal in 'application/x-www-form-urlencoded' content, they completely omit the part saying that GET request query strings are defined as that type. There is, in fact, no mention whatsoever about the query string encoding in anything after the HTML 2.0 spec.
Which leaves us with the question - is it valid? Certainly there's a LOT of legacy code which supports '+' in query strings, and a lot of code which generates it as well. So odds are good you won't break if you use '+'. (And, in fact, I did all the research on this recently because I discovered a major site which failed to accept '%20' in a GET query as a space. They actually failed to decode ANY percent encoded character. So the service you're using may be relevant as well.)
But from a pure reading of the specifications, without the language from the HTML 2.0 specification carried over into later versions, URLs are covered entirely by RFC3986, which means spaces ought to be converted to '%20'. And definitely that should be the case if you are requesting anything other than an HTML document.
Source: Stackoverflow.com