Google does not use the Keywords meta tag to process the ranking of the sites that will be displayed in a search. In the link below you can check which meta tags the google robot uses to index the sites.
https://support.google.com/webmasters/answer/79812?hl=pt-BR
The Yahoo search engine uses this meta tag, but the words contained in it have less relevance than words from other places, such as those contained within the body, title, Description or Anchor tags.
Bing uses the same idea as Yahoo: meta tags are a sign, but with very little relevance.
If you have searchers in mind, using the keyword meta tag will not help. This tag has already become history :)
Looking at it from this point of view, in addition to the tags Description, title, H’s, what would be the best ways for SEO?
– Cobra
Regarding the searchers these are the most important! Surely the tag title is the most important of all! If the title is well chosen it will make quite a difference in indexing.
– Sérgio Mucciaccia