What a meta description is for
A meta description does not affect where you rank. It has not been a ranking factor for many years and no amount of keyword stuffing changes that.
What it does is decide whether the person who already found you clicks. Your page is sitting in a list of ten roughly similar-looking results, and the two lines underneath the title are the only argument you get to make. That is a click-through job, not a ranking job, and writing it as though it were the latter is why so many are unreadable.
The [msm_tool slug="meta-description"] drafts to a length that survives truncation, which is the first constraint but not the interesting one.
Google rewrites most of them anyway
This is the fact that changes how you should approach the task. Search engines frequently ignore the description you wrote and generate their own from the page, choosing whichever passage best matches the query someone actually typed.
That is not a failure and it is not something to fight. One page can rank for many queries, and a single fixed description cannot be the best answer to all of them. A generated snippet pulled from the exact paragraph that answers a specific search is often better than anything you could have written in advance.
Two practical consequences. First, write yours as the sensible default for your main query rather than trying to cover everything. Second — and this matters more — the quality of your actual page content determines the quality of the generated snippet, so a page with a clear, direct answering paragraph gets better snippets than one that buries its answer.
Length, and what actually gets cut
The commonly quoted figure is around 155 characters, and it is a useful target rather than a rule. Truncation is by pixel width, not character count, so a description full of wide characters cuts earlier than one full of narrow ones, and mobile results cut shorter than desktop.
The workable approach is to front-load. Put the substance in the first hundred characters or so and let anything after that be a bonus that some readers see. Then reread only the first hundred and ask whether it still makes a complete, useful statement.
Going long is not penalised — it is simply truncated, and a description that ends mid-word looks careless. Going very short is a wasted opportunity rather than an error.
Writing one worth clicking
- Answer the query. Someone searching a question wants to see that the answer is here. Saying so is more persuasive than any adjective.
- Be specific. A number, a version, a date or a constraint tells the reader this is a real page rather than a category of pages.
- Include the term naturally. Matched words are bolded in results, which draws the eye. That is the only reason to include the keyword — it is a visual effect, not a ranking one.
- Differentiate. You are next to nine other results. What does yours have that they do not: original data, a working example, a country-specific answer, an honest account of when the approach fails?
- Keep the promise. A description that oversells produces a click and an immediate bounce, which helps nobody and is visible in your own analytics.
Common mistakes
- Duplicates across the site. The same description on forty pages tells a searcher nothing about which one to open. If you cannot write a distinct one, that is often a signal the pages are too similar.
- Keyword lists. A comma-separated string of phrases reads as spam to a human and buys nothing from the engine.
- Starting with the brand name. The most valuable characters spent on something the title already showed.
- Describing the site instead of the page. We are a leading provider of… answers a question nobody in a results list is asking.
- Leaving it blank on important pages. Fine on a low-value archive; a missed opportunity on anything you want traffic to.
Where to spend the effort
Not everywhere. Descriptions are worth writing by hand for pages that already get impressions — the ones appearing in results and not being clicked. Search Console will tell you which those are: high impressions, low click-through, and a description that is doing nothing for you.
For everything else, a reasonable generated default is enough, and your energy is better spent on the page itself. A genuinely useful page with a mediocre description outperforms a thin page with a brilliant one, every time.
What you type goes from your browser to the provider you chose, under their terms, and never through this site.