Question

I’ve a really small website, so I usually update the sitemap by hand!
In each “url” element there are the fields: loc, lastmod, changefreq and priority.

The “lastmod” field is setup to the date in witch I update the content of the related PHP page or the content that is loaded dynamically in the related PHP page!

I’ve tried to use http://www.xml-sitemaps.com/ to verify if all it was right, and I’ve noticed that in the generated sitemap there isn’t the “lastmod” field!

In the Google wiki, about how to write a sitemap, there’s written that is a good practice to setup the “lastmod” field even for dynamic pages; so, my question is …

Is the “lastmod” field needed or not?

Thanks in advace!

Answer 1

The standard says that it’s optionnal : http://www.sitemaps.org/protocol.php#locdef :

<lastmod> optional

The date of last modification of the
file. This date should be in W3C
Datetime format. This format allows
you to omit the time portion, if
desired, and use YYYY-MM-DD.

Still, it might be usefull to let search engines / spiders know when your content was updated for the last time.

The How do I compute lastmod date? entry of the FAQ also gives an interesting reason, that explains why you should include the lastmod date if you can (quoting) :

Using even an approximate date or
timestamp can help crawlers avoid
crawling URLs that have not changed.
This will reduce the bandwidth and CPU
requirements for your web servers.