Using commas in URL's can break the URL sometimes?

Question

Is anyone aware of any problems with using commas in SEO friendly URL's? I'm working with some software that uses a lot of commas in it's SEO friendly URL's; but I am 100% certain I have seen some instances where some programs/platforms don't recognize the URL correctly & cut the "linking" of the URL off after the first comma.

I just tested this out with thunderbird, gmail, hotmail & on a SMF forum with no problems; however I know I have seen the issue before.

So my question is, is there anything in particular that would cause some platforms to stop linking URL's with a comma? Such as a certain character after the comma?

Solution

There will be countless implementations that will cut the automatical linking at that point. As with many other characters, too. But that’s not a problem because of using these characters, but because of a wrong/incomplete implementation.

See for example this very site, Stack Overflow. It will cut off the link at the * when manually entering/pasting this URL (see bug; in case it gets fixed, here’s a screenshot of it):

• http://wayback.archive.org/web/*/http://www.example.com/

But when using the hyperlink syntax, it works fine:

• http://wayback.archive.org/web/*/http://www.example.com/

The * character is allowed in an HTTP URL path, so the link detection should have recognized the first URL instead of breaking it at the occurence of *.

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Regarding the comma:

The comma is a reserved character and its meaning is relevant for the URL path (bold emphasis mine):

Aside from dot-segments in hierarchical paths, a path segment is considered opaque by the generic syntax. URI producing applications often use the reserved characters allowed in a segment to delimit scheme-specific or dereference-handler-specific subcomponents. For example, the semicolon (";") and equals ("=") reserved characters are often used to delimit parameters and parameter values applicable to that segment. The comma (",") reserved character is often used for similar purposes. For example, one URI producer might use a segment such as "name;v=1.1" to indicate a reference to version 1.1 of "name", whereas another might use a segment such as "name,1.1" to indicate the same.

So, if you don’t intend to use the comma for the function it has as reserved character, you may want to percent-encode it with %2C. Users copying such an URL from their browser’s address bar would paste it in the encoded form, so it should work almost everywhere.

However, especially because it’s a reserved character, the unencoded form should work, too.