Use of Parentheses in HTML with "href=tel:"

Good question. Finding a clear, authorative answer regarding href="tel:" specifically is difficult.

RFC 3986 (Section 2.2) defines parenthesis as "reserved sub-delims". This means that they may have special meaning when used in certain parts of the URL. The RFC says:

URI producing applications should percent-encode data octets that correspond to characters in the reserved set unless these characters are specifically allowed by the URI scheme to represent data in that component. If a reserved character is found in a URI component and no delimiting role is known for that character, then it must be interpreted as representing the data octet corresponding to that character's encoding in US-ASCII.

(Emphasis mine)

Basically, you can use any character in the US-ASCII character set in a URL. But, in some situations, parentheses are reserved for specific uses, and in those cases, they should be percent-encoded. Otherwise they can be left as is.

So, yes, you can use parentheses in href="tel:" links and they should work across all browsers. But as with any web standard in the real world, performance relies on each browser correctly implementing that standard.

However, regarding your example (<a href="tel:+33(0)...), I would steer clear of the format you have given, that is:

[country code]([substituted leading 0 for domestic callers])[area code][phone number]

While I was unable to find a definitive guide to how browsers handle such cases, I think you will find, as @DigitalJedi has pointed out, that some (perhaps all?) browsers will strip the parentheses and leave the number contained therein, resulting in an incorrect number.

E.g.

<a href="tel:+33(0)1234567890">+33 (0) 123 456 7890</a>

will/may result in a call to +3301234567890. Will this still work? Maybe? We're getting into phone number routing territory now.

Some browsers/devices may be smart enought to figure out what is intended and adapt accordingly, but I would play it safe and instead simply use:

[country code][area code][phone number]

E.g.

<a href="tel:+331234567890">+33 (0) 123 456 7890</a>

There is no downside (that I know of) to having your local users dialing the international country code - it will result in the same thing as if the had omitted it and substituted the leading zero.

Here is some semi-related, useful information regarding browser treatment of telephone links: https://css-tricks.com/the-current-state-of-telephone-links/

The () in the href attribute should not be a problem: (href-wise)

http://example.com/test(1).html

HOWEVER, if I do a href="tel:+000 (1) 000 000", after clicking the link on phone, the dial on my phone will show +0001000000 This is tested and confirmed on a Android device

This means that the parentheses are removed, as well as the spaces.

But this could still vary because of different OS on the phone.

P.S.:

If you think the + in your number is an issue... I did test this too, and the + does not have any unexpected behavior.

MORE: href="tel:" and mobile numbers

According to ITU-T E.123 Section 7.2 Use of parentheses

The ( ) should not be used in an international number.

So (0) should not be included at all.

I read and remember the correct format should be: +33.1 23 45 67 89 But I can't find where from.