What the counter measures
The length and character counter takes the copy you paste in and gives you a running count of characters and words. It is a plain counting tool: it doesn't judge the copy, and it doesn't know which platform you're writing for unless you tell yourself by checking the number against a limit. What it does is remove the guesswork of counting by eye, which is where most length problems creep in unnoticed.
That sounds like a small thing until you've written a headline that reads perfectly on screen and then gets cut off mid-word in a search result or an email inbox. A character counter catches that before it happens.
Why the character count matters more than it looks
Most commercial formats have a hard limit set by someone else: the platform, the inbox provider, the ad network. Go over it and the reader doesn't see an error message, they see your sentence with the end missing, and a headline that stops halfway through a word says nothing at all. The reader's eye takes in whatever fits, so a limit isn't a guideline you can round up from, it's the point past which your copy simply isn't there any more.
This is different from the word count you might use to judge a paragraph's readability, which is about pace and comprehension rather than a hard cut-off. A subject line or an ad headline lives or dies by characters, because that's the unit the platform actually measures. A body paragraph lives or dies by whether the reader can follow it, which is a job for the Readability and Clarity Checker.
Where the limits themselves come from
Google Ads headlines, meta descriptions, email subject lines and social post captions all carry limits, and each platform sets its own, changes it occasionally, and enforces it slightly differently. Giving specific figures here would go stale the moment a platform updates its rules, so this guide doesn't repeat them. Copy Length Reference Tables sets out the current figures with a source and a date, which is the better place to check before you write to a specific limit.
Cut the padding before you cut the claim
When a line runs over, the instinct is often to shorten it from the end, and that's usually the wrong place to cut. The words worth losing first are the ones doing no work: really, very, a wide range of, innovative. The words worth keeping are the ones carrying the actual fact, the noun and the verb that tell the reader what happens.
Take a subject line that runs long: 'Save money and time with our brand new innovative approach to invoicing today.' Cut the filler and what's left is 'Cut your invoicing time in half', which is shorter, fits the limit, and says more, because every word left is doing something. The first version was padded; the second is trimmed to the claim itself.
A rule worth keeping: when you need to lose characters, look for adjectives and stock phrases before you touch the verb or the specific detail. Losing 'innovative' loses nothing a reader would have believed anyway. Losing 'invoicing' loses the entire point of the sentence.
What the count can't tell you
The number you get back will be right for the text you pasted in, but it can't tell you how a platform will actually display it. Some services truncate by character, others by word, and search snippets are measured in pixel width against a variable font rather than a fixed character count, so two headlines of the same length can be cut at different points. Treat the count as a working guide for drafting, not a guarantee that the platform will show every character you've written, and check the live preview on the platform itself before anything goes out.
Where to check the term or the next step
If a term in this guide, such as above the fold or CTA, needs a fuller definition, the Copywriter's Glossary is the canonical source. Once your copy fits its limit, running it through the Headline Scorer checks whether it also does its job within that space.