The SEO crawler that won't stay quiet about your site's problems.
Pulls the title and description off any page and shows the result they produce. Edit them and watch it change.
It fetches the page, reads its <title> and meta description exactly as the server serves them, and draws them as they would appear in a Google result. Then it measures them.
In pixels, not characters. That is the difference that makes a preview worth having: Google truncates by width, and letters are not the same size. "Illinois" and "mmmmmmmm" are both eight characters and one is nearly twice as wide as the other. Counting characters gives you a limit that is sometimes generous and sometimes wrong.
A title that fits is not a title that shows. Google rewrites a substantial share of them when it thinks something else matches the search better, usually pulling an h1 or the site name. The description is looser still: it is a suggestion, and a snippet is often assembled from the page's own text instead.
Does the meta description affect rankings? It is not a ranking factor. It affects clicks, which is a different thing and also matters: the same position with a better description earns more visits.
How long should it be? There is no official number. What works is putting the important part first, so it survives the truncation — which is harsher on mobile than on desktop.
I have no description. Is that a problem? Google will assemble one from the page. Sometimes it reads well. What you lose is the choice of which sentence represents the page in the results.