I have recently seen a few URIs containing the query parameter "utf8=✓". My first impression (after thinking "mmm, looks cool") was that this could be used to detect a broken character encoding.

So, is this a better way to resolve potential problems with character encoding, or is it just a developer having fun with a hack?

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    I disagree. There are schemes out there that look like URNs and that take query parameters - such as Bitcoin. URIs are not confined to browsers. See en.wikipedia.org/wiki/URI_scheme. This question may also address the general case where character encoding is required when a browser accesses a protocol handler. – Gary Rowe Oct 19 '12 at 8:29
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    Give examples of these URLs or didn't happen. – hakre Oct 22 '12 at 12:59
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    Off topic, but OK. Here's my personal donation Bitcoin URI: bitcoin:1KzTSfqjF2iKCduwz59nv2uqh1W2JsTxZH?amount=0.5&label=Agile%20Stack. Notice that the scheme is essentially a URN with query parameters, but it hands off to a protocol handler. This kind of URI could probably benefit from the “utf8=✓” workaround as well. – Gary Rowe Oct 22 '12 at 17:47
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    @GaryRowe So did you ever get any donations off that link? – Kyralessa Sep 18 at 10:30
up vote 804 down vote accepted

By default, older versions of IE (<=8) will submit form data in Latin-1 encoding if possible. By including a character that can't be expressed in Latin-1, IE is forced to use UTF-8 encoding for its form submissions, which simplifies various backend processes, for example database persistence.

If the parameter was instead utf8=true then this wouldn't trigger the UTF-8 encoding in these browsers.

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    @LarsViklund I should have been clearer with my comment. I meant that the validation associated with character encoding is simplified, not bypassed. – Gary Rowe Oct 13 '12 at 13:48
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    @Lars Correct, it doesn't absolve you from having to check your input. But it does mean that encoding tweaks only become part of your security handling and don't taint the concept of your "standard processing" path – Gareth Oct 14 '12 at 10:08
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    Also see stackoverflow.com/questions/3222013/…. Apparently Ruby on Rails used to use a snowman character, and was changed to a checkmark which was less ambiguous but less funny. – Jack V. Oct 17 '12 at 10:06
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    @JohnLBevan it's ignored by the receiving end, it's done it's job to force the browser to send things in utf8 instead of latin1. I've also seen it as ie=💩 (that's the 'pile of poo' code point, looks like it's not rendering in comments.) – cabbey Oct 18 '12 at 19:54
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    @Gareth: Can you back-up the statement that IE <= 8 forms do not support the document and/or form encoding? – hakre Oct 22 '12 at 13:00

protected by user40980 Nov 18 '13 at 19:58

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