API stands for application programming interface, which is the intermediary code that allows applications to talk to each other. All major ad platforms have APIs, and with a little know-how, you can write pieces of code that will help you manage your advertising better.

On most platforms, APIs automate certain processes that you’d otherwise have to do manually. On Facebook, however, the API functions a little differently and is more powerful because it contains features that you simply can’t access via the Facebook Ads interface.

Without coding experience, API documentation can be difficult to understand. Keeping that in mind, let’s take a look at the parts of Facebook Ads that are only accessible via API — and discuss when it might be worth diving into them. 

Advanced Interest Searching

When you’re searching for interested audiences in the Facebook Ads interface, you’re directly querying Facebook’s Targeting Search API.

Given a collection of letters or words, this API will return a list of “interest audiences” that match your query. For example, if you start typing a word like car into the interest audience search bar inside an ad set, you’ll see results like car racing, car rentals, and electric cars.

But there’s more to it: Facebook Ads only lets you see 25 interest audiences for any search. This isn’t because the Targeting Search API only returns 25 audiences; it’s because Ads Manager artificially limits what you see to the first 25 results.

This is particularly limiting if you are trying to: 

• Research which audiences are available
• Target more niche audiences, which might not appear within the first 25 results 

If you query the API directly instead, you see every interest audience that’s relevant to your search. From here, you can simply add these to your ad sets.

If you’re interested in learning more about interest audience searches, here’s the relevant API document.

Bid Modifiers

If you’re advertising a product where LTV is important, then you likely know the factors that influence LTV. You might know, for instance, that women using your brand have a 20% higher LTV than men, or that LTV increases steadily with user age.

While this is good contextual information, it can be difficult to translate into actionable strategy. You might be tempted to take advantage of it by creating different campaigns for each age and gender combination, working toward a different CPA for each. This would be highly complex to manage though, not to mention the small size of each campaign will limit how much you learn.

A better solution is to use Facebook’s bid modifiers API. This lets you run a single ad set targeting any audience you want — all while working to different CPA targets for each segment.

As a basic example, you might run an ad set targeting males and females, working towards a CPA target of $10. If I happened to know that females had a 20% higher LTV, I could apply a +20% bid modifier to females, and effectively work towards a $12 CPA for them. This lets you work towards different LTVs for different audience segments, without having to fragment your campaign. 

The bid modifier API has been around for more than a year, but is still in closed beta phase. You can reach out to your Facebook rep if you’re interested in getting access.

Custom Experiments

Facebook’s experimentation tools have come a long way in recent years. The experiments tab within Ads Manager now allows for complex, multi-cell tests, both with and without holdout groups (otherwise known as lift tests).

Long before these features were available in Ads Manager though, they were accessible via the Facebook API. To this day, there are still some experimentation options that you can only access via the API:

• Custom cell sizes. A cell is one section of a test. A standard A/B test between two campaigns is referred to as a 2-cell test, for example, in which each cell contains one campaign. When creating experiments via the API, you can customize how much traffic goes to each cell. Break it up to run 80/20, 90/10 tests and so on, rather than just plain 50/50. This can be useful where you’re testing a high-risk variant, and want to limit the amount of traffic that variant receives.
• Advanced lift test reports. Any lift tests created via the API will give you access to much richer reporting functionality, allowing you to break your results down by demographic segments. This can be useful for large-scale lift tests, where you have enough data to determine cost per incremental conversion by age or gender.

You can find more information on these features in the split testing and conversion lift API documents.

Advanced Lookalikes

Lastly, we have lookalike audiences. Building your lookalike audiences through the Facebook API gives you two main advantages over building them through Ads Manager’s audience screen:

• Advantage 1: 20% Lookalikes. Ads Manager allows you to create 0-10% lookalike audiences through Ads Manager (this means audiences comprising 10% of people within a country that most closely resemble some predefined seed audience). Within the API, you can take this up to 20%.

This can be useful when you’re looking to run broader campaigns (broader than a 10% lookalike), but want to stop short of targeting a whole country. These 20% lookalikes can also be layered on top of specific interest audiences, helping refine your audience without overly restricting volume.

• Advantage 2: Smaller Minimums. Ads Manager requires your source audience to contain 100 people from a specific country in order to create a lookalike from it. But within the API, you can create lookalikes in one country based on users in another country. This is particularly useful where you’re launching in a country for the first time, and don’t have any existing users in that country to base your lookalikes on.

You can find out more on how to take advantage of these two features in the lookalike API docs.

Knowing Where to Look 

Clearly, there is more to advertising on Facebook than just the Ads Manager platform. While navigating the API and relevant documentation can be a little technical, it can also be very valuable for advertisers. Not every API-only feature will apply to each advertiser, but it’s good to be aware of them when you do run into potential use cases. While some of these features will get built into Ads Manager over time, some of them will likely remain hidden in the API — and only available to advertisers who know where to look.