Currently, the favicon is called from a static source within the root directory. It might make sense to have a dynamic path for this which also allows hosting images on different sources like a CDN.
manpageblog should also support HTML meta keywords which could also be used as tags. This should be set for each site independently to have a better SEO rating.
A feature regarding meta robots support should be integrated to give users the possibility to define a robot option for each website. There might be cases where subsites or pages should not be indexed (e.g. imprint, data policy,...).
Not every option within the config file is mandatory. Therefore, manpageblog should check for mandatory options and throw an exception and also ignore missing optional options.
Thanks for Wojtek for mentioning me in the Fediverse, that manpageblog should also include a link tag for application/rss. This may be needed to indicate that the website is able to deliver RSS feeds. This may also be important to give users a possibility to catch the feed url since there isn't any visible hint for.
Task
Add the link tag according to the used domain to the header <link rel="alternate" type="application/rss+xml" title="RSS Feed for $URL" href="/rss/" />