With cleaning the formatting, if the text was copied from another source, and with counting its length – these two steps set the frame for everything else that follows.
No. It is useful where there is a chance of a rich snippet: products, rated articles, frequently asked questions. For an ordinary informational page, markup does not give a noticeable effect.
Density is the share a keyword takes up in the total length of the text. The same number of occurrences gives a different density in a short text and a long one, so it should be judged by percentage, not by a raw repeat count.
As a rule, no: changing the address creates a new page as far as a search engine is concerned. The address is worth thinking through in advance, before publishing.
This section gathers tools for working with the text on a page and with what a search engine shows about it in the results: from counting characters and cleaning text to generating titles, descriptions and structured data.
One part of the tools works with the body of the text – typing it up, cleaning it, counting it, comparing versions. The other works with metadata that is not seen by the reader but by the search engine: the title, the description, structured data, the URL slug.
This is also where the utilities used more often while preparing content than while writing it are gathered: the QR code generator for offline materials linking to an article, the image converter for illustrations, and the color picker for matching a palette to a brand style.
If the task is not about text but about a page's technical state, check the Technical SEO & Security section. To gauge demand for future text and the rankings of already published articles, see Search Analytics & Research.