What is <last mod>, aka Last Modified, for in an XML sitemap?
If your website has an XML sitemap (and yes…you should really have an XML sitemap), Changefreq is an optional sitemap tag that supplies key data to the search engines and now Large Language Models. It communicates how fresh your content is, which has various implications in the SEO / GEO field. We consider it an SEO best practice when we conduct an SEO audit for clients.
Does adding <last mod> help with SEO ?
First of all, it certainly doesn’t hurt. But yes, adding <last mod> can help improve your SEO visibility as it helps Search Engines crawl and understand your website better. Bing also tends to prioritize fresher content in its ranking system and stated <last mod> is a top signal for AI tools. However, it’s important to note that, like many great tactics of yesteryear, black hat SEOs came up with spammy tactics to make it look like content was fresher than it was – if you do that, then it’s not going to help you (and may even hurt). The key is that it needs to be consistent and verifiable.
Does adding <last mod> help with GEO or visibility in AI search engines?
GEO is a rapidly developing field, but there are early studies that suggest that adding <last mod> to your XML sitemap might be a helpful tactic to utilize. It’s also very quick and relatively easy to implement while also being low risk, meaning the potential ROI of this tactic is quite high.
However, what these studies also specify is that LLMs prefer fresher content, so adding <last mod> but not actually adding fresh content to the website won’t help.
Should I still use other optional tags in my XML Sitemap, such as ChangeFreq & Priority?
You can probably skip them. Google ignores <changefreq> and <priority>, and Bing notes that it largely disregards these settings. In addition, LLMs also don’t depend on sitemaps the same way search engines do, which is why the industry has been buzzing about llms.txt, which is essentially a sitemap delivered in a format that is useful for LLMs (however, there is little to no evidence that LLMs.txt files actually deliver any value for GEO either).