How do ads work in paid search?

With keywords covered, let's now look at ads, and the role they play in paid search. For a brief refresher, ads appear on a search results page (SERP) when a keyword in the same ad group wins an auction. If there's only on ad in the ad group, that ad will be chosen 100% of the time. If there are multiple ads in the relevant ad group, only one will be chosen to display on the SERP (we'll cover how that ad is chosen later on).

What actually is an ad?

An ad is made up of lots of different parts. Each part of the ad is listed in the image below:

How do ad headlines work?

Ad headlines are arguably the most important part of your ad. They're the most visible to the user, meaning they have the most impact on metrics like CTR. They're also heavily prioritised by search engines when it comes to assessing ad relevance, meaning that you need your headlines to be relevant in order for your ads to be relevant.

Headline 1 in particular is the part of the ad that's most important for assessing ad relevance. As such, it's often a good idea to try to map your headline 1 as closely as possible to the keyword(s) in your ad's ad group.

This isn't as simple as just putting the keyword in the ad copy. For example, if your keyword is [running shoes buy], you wouldn't want a headline 1 of Running Shoes Buy.

You'd want to change it to something like Buy Running Shoes, so that it contains exactly the same words as your keyword (ensuring ad relevance) but in a more grammatically correct order (which is likely to improve CTRs).

There are a couple of other important things to know about headlines:

How do ad descriptions work?

Below your headlines come your descriptions. Descriptions are much longer, letting you write up to 90 characters worth of text. This means you have more of an opportunity to really sell your brand here.

Descriptions don't typically get as much attention from users as headlines, owing to the fact that they're less prominently displayed on the SERP. They also aren't as important as headlines when it comes to assessing ad relevance, meaning there's less of a need to tailor them to their ad group's keywords. By all means, tailor them if you can, but this doesn't have to be done very granularly.

Just as with headlines, there are a couple things to keep in mind when it comes to descriptions:

How do ad URLs work?

Each ad can have a URL associated with it, such as Of course the URL doesn't have to just be a base domain (like, it can also include a path ( This URL, the URL where clicks are sent to, is called the ad's final URL.

In addition to determining where clicks get sent to, the ad's final URL also impacts what URL the searcher sees in your ad. The URL that appears in your ad will always have the same base domain as your final URL. So, if your final URL is, then the URL that appears in your ad will start with

There are two fields which exist at an ad level which allow you to customise how your ad's URL appears to searchers, display path 1 and display path 2. If your final URL is, then (regardless of what part of your final URL is set as) your ad's URL will take the format: path 1/display path 2.

What's crucial to understand here is that display path 1 and 2 have no effect on where your traffic goes to. That's fully determined by your final URL, which just contributes the base domain to the ad URL. Display paths serve two specific purposes:

While you're going about crafting display paths that appeal to users, and boost your ad relevance, there are a last few things to bear in mind:

Final URLs: keyword or ad level?

I started this section on URLs by saying that each ad can have a final URL associated with it. Strictly speaking though, ads don't need final URLs. The reason for this is that you can also set final URLs at a keyword level. All that's required in order to run paid search is that, for each ad group you're running, either all the keywords in that ad group have final URLs or all the ads in that ad group have final URLs.

This isn't an exclusive 'or'. You can set keyword level final URLs and ad level final URLs. In this case, the keyword level final URL will overwrite whatever is set on the ads. To make this a little less abstract, let's give an example.

Say that I have an ad group with one ad and one keyword. My ad's final URL is, and my keyword's final URL is If I was to put the ad group live, all the traffic it generated would be sent to, because the keyword final URL overwrites the ad final URL. Nothing would happen if I removed the ad final URL, however if I removed the keyword final URL then all traffic would be sent to

All this begs the question: should you set your URLs at keyword or ad level? Personally I always advocate for setting final URLs at ad level, and leaving your keyword level URLs blank. The reason for this is that there's no benefit to setting keyword level URLs, but one small benefit to setting ad level URLs.

This is that, if you want to test multiple different landing pages within an ad group, you'll need to do this by creating multiple ads with different final URLs. How exactly you'd do this is something we'll cover later on, but suffice to say that it requires your final URLs to be set at ad level.

Ads: in summary

Let's take a second to do a quick roundup of what we've learnt about ads. They have three main parts; headlines, descriptions and URLs. Each of these can be further broken down, i.e. into three different headline spots, two description spots, and an ad URL can be broken down into a domain plus two display paths.

Each of the different parts of the ad come with different character restrictions, but they all contribute to ad relevance. We saw in the auction section how fundamental a role ad relevance plays in determining performance, so it's vital to craft ads that are relevant to their ad group's keywords.

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