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[Cormac]

(that is technically not the right term but anyway...)

Do websites which alter their file extension from .php to .daft for example (Daft.ie : Place ad on Daft) get penalised in anyway from search engines as they're not using a standard extension?

Or is this a good practice in the sense that you can have a keyword in each and everyone of your file names. For example 169themall.com/index.shop for a shopping site.

 

[RedCardinal]

Completely new page in the eyes of a SE.

To retain ranking etc. you need to set up a 301 redirect from old .php page to new .daft page.

No penalty AFAIK. You are free to call your page anything you like an as long as you keep within the guidelines you'll be good to go.

SEs give weight to keywords in URLs for sure

 

[Cormac]

and i'm sure having a keyword has a file extension makes it all that bit better