Interoperable Top Level Domain Name Parsing comes to IE

As part of our ongoing commitment to help build an interoperable Web that “just works,” we are changing the way Top Level Domains (TLD) names are parsed to use the Public Suffix List. This change can be previewed using Internet Explorer in the Windows 10 Technical Preview.

In the past, IE used a custom algorithm and kept a private list of domain name parsing exceptions. Owners of domain names that needed exception handling by our algorithm had to notify Microsoft that exception parsing was required.

Going forward, to increase interoperability we are switching our parsing to use the algorithms and domain list found at, which is a cross-vendor initiative also used by other browsers. Starting with the Windows 10 Technical Preview, IE will parse domain names in a more interoperable manner. After this change has been released in a product release you will no longer need to notify Microsoft of special domain names; we will automatically pick up and include the changes made at on a regular cadence. We are also evaluating bringing this change downlevel to accelerate the transition.

Join the Windows Insider Program to try the new top level domain name parsing in IE and let us know if you have feedback @IEDevChat or on Connect.

— David Walp, Senior Program Manager, Internet Explorer

Comments (6)
  1. Joseph says:

    What is the TLD parsing needed for?

  2. jimmy says:

    Wow…. The fact that this list has to exist makes me want to cry….

    But thanks for at least using the same list as everyone else now guys!

  3. Brenno says:

    I thought with the recent influx of new TLDs manual lists are going to get phased out since they don't scale anymore.

    @Joseph: Same-origin policy, e.g. what domain level a cookie can be set for.

  4. Gervase Markham says:

    Brenno: there is as yet no feasible replacement for As long as Microsoft implement the algorithm correctly (i.e. if they see a domain that's not in the list, treat it like .com – i.e. flat namespace) then it's not a massive disaster if new gTLDs take a little while to percolate into the system, because most of them are flat like that anyway.

    Gerv (PSL maintainer)

  5. Brenno says:

    Thanks Gerv. Yeah, from a security standpoint the possibly slow percolating (smartphones/tablets?) is certainly not going to be a problem. It might be a bit of a challenge to those companies getting their own TLD but maybe it serves them right. 😀

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