Write the sentence that earns the click
A description is advertising copy in the most literal sense: it sits under a title, next to nine competitors, and its only job is to make yours the one someone chooses.
What works is specificity. "Learn about our range of services" says nothing that the other nine do not. "Compare 40 mortgage rates and see the monthly payment for each" tells someone exactly what they get.
Truncation eats the end
Around 920 pixels on desktop, considerably less on mobile. Two consequences:
- The first sentence must work alone, because on a phone it may be all there is
- Do not put the call to action last, where it will be cut
When Google overrides you
It happens most when the query matches text on the page better than your description does — often on long-tail queries you did not write for. That is usually a better result for the searcher, and it is not a failure of your tag.
The description is worth writing for your main query. It is not worth agonising over for the hundred queries you cannot predict.
Questions
Google rewrites descriptions anyway — why bother?+
Because it rewrites them on some queries and uses yours on others, and you only control one of those. When it does use yours, it is the sentence that decides whether someone clicks. When it does not, nothing is lost.
Does the description affect ranking?+
Not directly, and it has not for many years. It affects click-through, which is what it is for. Stuffing keywords into it helps nothing and reads badly in the one place it is shown.
How long should it be?+
Around 920 pixels on desktop, which is roughly 150–160 characters for typical text — but the width is the real constraint, which is why it is measured here. Mobile shows less, so the first sentence should stand alone.
Should every page have one?+
Every page you want clicked from search. For a page with no natural summary, letting Google build a snippet from the content often produces something better matched to the query than a generic sentence would be.