While playing around with RSS feeds on Stack Overflow I came across a bug when trying to get a feed for the c# tag.

If you go to https://stackoverflow.com/feeds/tag?tagnames=c%23&sort=newest you will see that it takes you to the feed for the c tag instead. Using the shorthand https://stackoverflow.com/feeds/tag/c%23 responds in the same way.

The first feed URL came from the bottom of C# tagged questions page.

EDIT: If you try to escape the % as well it will work for the long URL but not the short. https://stackoverflow.com/feeds/tag?tagnames=c%2523&sort=newest pulls up the c# tag feed, but https://stackoverflow.com/feeds/tag/c%2523 returns a blank page.

EDIT 2: It appears to be in Chrome only. Just tested other browsers (Firefox, Safari, IE8, Opera) and they work as expected.

  • Based on your edit, I would say this is a bug in Chrome, not in the RSS feed software.
    – Randolpho
    Commented Mar 30, 2010 at 15:56

2 Answers 2


Both of your links point to the C# newest and active feeds, not the C newest and active feeds.

  • 2
    That's what I get for not testing all possibilities. Chrome can be a pain sometimes.... Thanks for making me actually... check my work! :)
    – Joshua
    Commented Mar 30, 2010 at 15:52

What is c%2523 ?

Checking my ASCII chart, let's see:

25 = %  
23 = #  

So after doing a little conversion, these URLs are in the form of

/feeds/tag/c%2523 ---> /feeds/tag/c%23

So these are just.. invalid. How did you get them?

  • @Jeff Atwood: I think "c%2523" came from the perceived notion that the URL is descaped twice. Descaping the percent in "c{%25}23" (braces added for emphasis) results in "c%23", which might then be descaped a second time to "c#".
    – Randolpho
    Commented Mar 30, 2010 at 20:46
  • @rand ok, fair enough, where is that link created on our own site? I guess if it's chrome only then it's a browser issue by definition..? Commented Mar 30, 2010 at 21:52
  • I don't think that URL is generated by SO. I think @Joshua was trying to figure out the problem and thought "hey, maybe it's double-descaping the url!" and hand-escaped the % character, giving him "c%2523" as a means of "testing" the RSS feed. I also think his test likely indicates that chrome has some issues with url escaping.
    – Randolpho
    Commented Mar 30, 2010 at 22:00
  • 1
    @Randolpho, @Jeff Atwood: Correct. The double-escaping was my own test to see what could be causing the problem. The # is a reserved character in a URL string so Chrome is just throwing it away when requesting the resource, sending /tag/c instead of /tag/c#. My guess was that Chrome was unescaping the string before sending it to the server, found the # and stripped it, then sent the request; so I double-escaped it so it would translate to %23. All-in-all, it's seems to be a bug with chrome.
    – Joshua
    Commented Mar 31, 2010 at 14:33

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