What is an Ad Server? The Definitive Guide for 2021

An ad server plays an important role in digital advertising, but thanks to the abundance of programmatic tech like DSPs and SSPs, there's a lot of confusion around what exactly it does.

This article dives into what an ad server is, as well as lists the Top 10 Best Ad Servers.

Table of Contents:

1. 1. What is an Ad Server?
2. 2. Ad Servers vs Ad Networks
3. 3. Ad Server Features
4. 4. How to Get an Ad Server
5. 5. The 10 Best Ad Servers

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What is an Ad Server?

An ad server is the ad technology that enables the management, serving, and tracking of an ad or internal promotion on one's digital properties. Ad servers decide, in real-time, the best ad to serve based on relevance, targeting, budgets, and revenue goals.

There are two types of ad servers: publisher-side (or, sell-side) and advertiser-side (or, buy-side). While similar tech is involved, the use cases are very different:

	Publisher-Side	Advertiser-Side
Purpose	Serve and manage ads appearing on one's own digital properties	Easy creative management and tracking of one's ads as they appear on another publisher's website/apps
Used by	Sales, ad operations, or end-users (if it's a self-serve platform)	Marketers
Main value	Helps monetize one's digital properties; allows publishers to easily store and manage what ads appear on their site/app	Improves marketing paid spend performance through real-time creative optimizations and easy creative rotation; provides independent tracking metrics

In general, third party ad serving vendors specialize in one or the other, although some brands do cater to both uses.

The rest of this post dives into publisher-side ad servers

What is a publisher-side ad server?

A publisher-side ad server is the tech that enables:

1. The insertion of ads/promoted content into your digital properties, including direct-sold ads, programmatic ads, and house (internal) ads
2. The storage and management of the ads that'll appear
3. The setting of rules to determine what ads appear when and where (including targeting, priorities, and pacing)
4. The selection of the best ad to show using an ad decision engine
5. The tracking and reporting of the campaigns

Also, as a point of clarification, if you are working with a programmatic partner (SSPs/DSPs/etc), then some of these steps are done by them, not by your ad server. But an ad server would manage all those pieces for direct-sold ads and internal promos.

Why should I have an ad server?

There are multiple reasons to pursue an ad server:

1. You want to monetize your digital property Perhaps you are a social network with a huge user base but no revenue, or a news site that can't grow via subscriptions. Regardless of your situation, any publisher with digital real estate can make (more) money by selling ads on its properties. To do this, you can place standard banners on your site or create customized native ads that mirror the look and feel of organic content (like Facebook, Pinterest, Reddit, EA, and many others have done).
2. You want to integrate sponsored listings into your marketplace/eCommerce site Many eCommerce brands / marketplaces (like Etsy, Amazon, ebay, and Yelp) have built ad servers that enable vendors/sellers to pay to promote their organic listings in search and browsing results. These sponsored listing ads provides an incremental revenue stream without impacting the user experience.
3. You want to cross-sell or promote internal content / house ads An ad server doesn't have to serve just "ads". Many publishers use ad serving infrastructure tech to cross-sell products across their different properties, upsell paid plans, send targeted messaging to individual users, advertise the most relevant products, optimize what products appear first in a list, etc.
4. You want to include email ads into your emails/newsletters If you are sending emails to a large user base on a regular basis, why not make a little additional revenue by inserting native ads into each email?

This strategy is often used by eCommerce brands, whose vendors pay to be promoted in daily/weekly emails.

Can you give a concrete example of an ad serving platform?

Yes! Let’s say I’m the owner of GoalTrackr, a tool for monitoring your spending habits.

My board is angry about our lack of subscription revenue growth, so I decide to supplement our income by selling ads inside our dashboard. I begin by chatting with banks, who would like to promote their credit cards.

I first contemplate whether I can just use our content management system (which manages everything else the user sees) to insert the ads into the dash. Unfortunately, in chats with the advertisers, it's clear they won't spend unless I offer:

• Frequency capping to target people only twice per day
• Pacing rules to ensure we hit $10K/month, spending evenly every day
• User-level targeting to target people by the # of linked accounts

This complexity is not something I can do with my CMS, so I realize I need ad server software.

And since I want native ads that won't ruin the user experience, I decide to build the ad server myself. Rather than spending a year on the project, I use third-party cloud tools such as Kevel to cut down my build time and launch in just a couple of weeks.

Once it's built, I upload my advertisers' creatives into the system, set up my targeting and business rules, and turn the campaigns on.

From there, the ad server does all the hard work of picking the right ad to serve within milliseconds, based on my advertisers' goals and my business rules. Revenue increases, and the board is happy!

How is an ad server different from a Content Management System?

A CMS is the tech that manages digital content. This can be home-built or a hosted service like WordPress or Drupal. While content management systems and ad servers are alike in that they manage the display of content, as mentioned above, the big difference is that an ad server includes an ad decision engine.

For instance, if you only had one advertiser, and they were appearing in the same spot to everyone, you could of course just use a CMS to insert this.

But simplicity isn’t the norm with ads; most publishers want to maximize revenue by selling to many advertisers, while also incorporating complex targeting rules to increase ad relevance and draw higher ad rates.

The ad decision engine is the magic that makes this happen. It ingests business rules defined by the publisher (such as enabling 1st-price auctions to increase CPMs) and advertiser goals (such as $20K spread evenly over a month), and then, out of 100s or even 10000s of ads, it chooses the right one to show in just milliseconds.

How is an ad server different from a network or exchange?

Ad networks/exchanges/SSPs/DSPS are all components of programmatic advertising, a way for advertisers and publishers to buy and sell ads at scale without direct relationships.

Usually a publisher installs some code onto their site/app, which sends a call to a programmatic partner, who then returns an ad to show. The publisher then gets paid for showing these ads.

The key difference between programmatic vendors and an ad server is that the latter enables the management of all ads: direct, internal promotions (house ads), and programmatic.

Indeed, it's possible to serve ads without using an ad server at all: just install an ad network's code onto your site and have them do all the work.

But if you wanted to manage direct-sold ads, in-house ads, and/or multiple programmatic vendors, you'll want an ad server.

Are ad servers just for desktop banner ads?

Not at all! An ad server can be used to manage any type of digital ad:

It should be noted that if you are working with an off-the-shelf ad server, it's unlikely it can accommodate use cases outside of standard banners.

For native or custom solutions (like out-of-home ads, map ads, in-game ads, etc), you'll want to partner with someone that does server-side ad serving, or build it yourself.

What is a self-serve ad server?

Many large publishers - such as Google, Facebook, Pinterest, LinkedIn, Reddit, etc - built ad servers that they then turned into self-serve ad platforms, where advertisers can sign-up by themselves, set up campaigns, and get reporting on performance.

Ad servers can therefore be public-facing, as long as you want to invest in building out the front-end.

What are some key features of an ad server?

The exact features of an ad server will depend on the vendor you use or what you build.

There is no ad server out there that includes all of the features mentioned below, but most will employ a majority of them. This is just a sampling; we have a more exhaustive list here.

Also, as mentioned above, if your focus is programmatic demand, some of these features are managed on the network/exchange/DSP side, not by the ad server.

Targeting Features

Type of Targeting	Example
Zone/placement	Location on page; spot in search results
Contextual	Shoes sub-category
Frequency capping	Show same ad only once to a user per day
Keyword	Ad appears in the search results for ‘red hat’
Day & hour parting	Show ads just on Saturdays, 9am-5pm
Country	USA, China
City/DMA	Durham, NC only
Demographic	Gender, age
Behavioral/interest	Shoe lovers (visitors who have searched for shoes in the past)

Ad Delivery/Decision Engine Features

Feature	Example
Ad pacing by time frame	Decision engine ensures a 30MM monthly impression goal is spready evenly across every day
Ad capping	A campaign gets paused after $500/day is spent, give or take just 1%
Goal optimizations	The advertiser bids via CPC but wants the system to optimize for a $20 cost per conversion
Priority waterfalls	Publishers can set rules so that premium direct sponsorships get priority placement, and if there's no ad to fill a spot, it'll move onto house ads
eCPM auctions	Rather than flat CPM or CPC pricing, the ad server picks the ad that will drive the most revenue for the publisher, using historical click-through-rates and current bids
2nd-price auction	A setting where the winning ad pays $0.01 more than what the 2nd-highest bidder bid

Campaign / Ads Management

Feature	Example
User interface	Hosted UI for campaign management, storing creatives, and reporting
Management APIs	APIs for programmatically creating/managing ads
Server-side ad insertion	APIs that provide bid responses in JSON so you can insert the ads into your CMS versus using JavaScript tags
Forecasting & sales reservation	For predicting future traffic and selling against that
Structured campaign hierarchy	Advertiser → Campaign → Ad Group → Ads
Campaign scheduling	Start on 9/15 and end on 10/15
Flexible ad unit options	So you can show 300x50 banners, native ads, email ads, out-of-home ads, etc
Macros	Tools that dynamically insert a user's location into the ad

Additional

Feature	Example
Tracking & reporting	Impressions, clicks, conversions, and custom events by advertiser, campaign, ad, etc
Third-party tag enablement	Including advertiser-side ad servers and brand verification tags, like Moat
GDPR compliance	Consent prompt and back-end database to store info
User management (advertiser logins)	A system for creating user logins, scheduled reporting, etc
Multiple server locations	Servers in Seattle, Singapore, etc, to ensure the fastest response times

A Visual Summary

Woah! That's a lot. And it's why trying to build an ad server from scratch (or trying to use your standard CMS) isn't going to be the most efficient path.

Seems interesting, but how do I get started integrating an ad server?

There are four main paths:

1. Build it yourself from scratch
2. Build it yourself using third-party cloud infrastructure tools
3. Self-host it with open source tools
4. Use a hosted, third-party solution

The pros and cons of each are:

Build it yourself

A company with plenty of engineering resources could build an ad server themselves and host it on their servers.

Pros	Cons
You can build exactly what you want, and there should be seamless integration with your organic content. You also don't have to rely on a third-party, who could change pricing or go under. It's this path that many successful publishers have taken: Google, Facebook, LinkedIn, Amazon, and so on.	It's going to be time-intensive and costly. Google and Facebook have 100s of ad tech engineers, for instance. You then have to maintain and continuously optimize the product. Trying to prioritize the project could also prove to be a hassle.

Build it yourself using third-party cloud infrastructure tools

Just like folks use cloud infrastructure tools for complex tech like telecom (via Twilio), finance (via Spreedly), and online chat (via SendBird), such tools exist for ad serving tool.

These ad serving API tools help brands build their own ad servers in weeks, instead of years.

Pros	Cons
You can create a fully-customized ad server with all the bells and whistles you want while cutting down build time by 90%+.	It still requires engineering resources. Substantially less than if building from scratch, but this path isn't an out-of-the-box ad server.

Host it yourself with open source tools

There are open source ad servers you can download for free or a nominal one-time fee. The scripts are then hosted on your servers and run by you.

Pros	Cons
You get quick access to an ad server architecture without having to pay a monthly vendor fee or worry about sharing your data with anyone.	There's still engineering work needed to host the script. The tools are also not very customizable, and there's no support team for troubleshooting.

Use a hosted, third-party solution

There are many SaaS ad servers out there, whereby you pay a monthly/yearly fee to access their ad serving tech. These out-of-the-box ad servers involve placing JavaScript tags on your site (or an SDK for apps), and then you use their UIs to manage your campaigns.

Pros	Cons
You can go live in hours without involving any engineers. Price is also competitive (Google's product is free for anyone with fewer than 90MM impressions). For basic ad serving requirements, these solutions provide all the needed functionality.	They are JavaScript-based (or SDK-based), which can slow down your page/app. They also offer limited flexibility and customization, so not ideal for native ads or anything that isn't standard banners. You are also sharing your data with a third-party.

The Best Ad Servers

1. Kevel

Type: Ad serving Infrastructure APIs

Kevel is the market leader in server-side ad serving, enabled through APIs.

With Kevel, brands can launch custom, fully-bespoke ad servers in a fraction of the time and cost of trying to build it from scratch. Companies expecting to build an ad server in months or a year can use Kevel to easily release the same one in just weeks.

Kevel's clients include Yelp, Bed Bath and Beyond, Ticketmaster, Edmunds, Mozilla, WeTransfer, and more.

G2Crowd: 4.5 stars

When to consider Kevel:

1. You care about page/app load times and want server-side ad calls instead of JS-tags
2. You want customization around the look and feel of your ad unit
3. You want full flexibility around business rules
4. You want a way to automate campaign creation, campaign management, and reporting
5. You want to build a self-serve ad platform
6. You are bringing your own demand
7. You have a non-standard ad unit, like billboard ads, VR ads, etc

When to think twice:

1. You want something you can set up in hours
2. You don't have any engineering resources
3. You want the ad server to provide programmatic demand

2. Google Ads Manager (GAM)

Type: Hosted third-party ad server

Of the popular ad servers, Google Ads Manager (previously DFP or DoubleClick for Publishers) is the leading third-party ad server by a wide margin, and it benefits from a seamless integration with Google's other ad products.

Capterra: 4.4 stars | G2Crowd: 4.0 stars

When to consider them:

1. You want a low-risk ad server. The Google ad server is not going to be shut down, probably ever
2. You want something inexpensive. If you have fewer than 90MM impressions a month, it's free. It's therefore the best free ad server on the market
3. Your focus is on programmatic revenue, as you'll get access to Google’s AdSense and AdX programmatic demand

When to think twice:

1. You need more customization than what an off-the-shelf ad server can provide
2. You want flexibility around the look/feel of the ads, targeting options, and more
3. You don't want to slow down your page/app by installing JS-tags/SDKs
4. You don’t like helping or enabling Google
5. You don’t like sharing your data with a third-party

3. Revive Ad Server

Type: Free, open source ad server

Revive Adserver, which spun out of OpenX many years ago, is a self-hosted ad server (via an open source script) you can download for free. After downloading, there is additional work needed to host and run the code. In 2019 they also released a hosted version.

Capterra: 4.2 stars

When to consider them:

1. You don’t want to pay a monthly fee to a vendor and like the idea of an open source ad server
2. You don't want to build an ad server yourself
3. You have the engineering resources to download, host, monitor, and update the code

When to think twice:

1. You need customer support. They have a community website, but you won't have a support team for troubleshooting
2. You need scale. Revive is a large script and requires a lot of ad server costs
3. You don’t have any engineering resources
4. You want to customize your ad server and have flexibility around ad units and targeting; an ad server open source solution won't have this
5. You don't want to slow down your page/app by installing JS-tags/SDKs

4. Smart Ad Server

Type: Hosted third-party ad server for programmatic ads

Smart Ad Server is a Google Ads Manager competitor whose selling point is its integration with an SSP for instant access to programmatic demand. Additionally, they are pre-integrated with multiple brand safety vendors, DSPs, and DMPs.

Capterra: 4.3 stars | G2Crowd: 4.0 stars

When to consider them:

1. You want to launch quickly without needing engineers
2. Your focus is on programmatic demand
3. You don’t want to work with Google or want better support than what Google would provide

When to think twice:

1. You need more customization than what an off-the-shelf ad server can provide
2. You want flexibility around the look/feel of the ads, targeting options, and more
3. You don't want to slow down your page/app by using JS-tags/SDKs
4. You want to easily do user-level targeting. Smart doesn’t provide turnkey access to a 1st-party DMP that can be used for ad targeting
5. You want APIs for ad delivery, reporting, and management

5. Adform

Type: Hosted third-party ad server for programmatic ads

Like Smart, Adform is a GAM competitor who focuses on programmatic-focused publishers. Their platform comes with detailed revenue forecasting, analytics for identifying new monetization opportunities, and bidding tools to maximize CPMs.

G2Crowd: 4.5 stars

When to consider them:

1. You want to launch quickly without needing engineers
2. Your focus is on programmatic demand
3. You want tools for understanding and optimizing all your programmatic partners
4. You want access to your own 1st-party Data Management Platform

When to think twice:

1. You need more customization than what an off-the-shelf ad server can provide
2. You want flexibility around the look/feel of the ads, targeting options, and more
3. You don't want to slow down your page/app by using JS-tags/SDKs

6. EPOM Ad Server

Type: Hosted third-party ad server for ad networks

EPOM is an ad server that caters to ad networks; their key value is around white-labeling and turnkey RTB integrations. They are also open to custom development.

Capterra: 4.4 stars | G2Crowd: 4.5 stars

When to consider them:

1. You are starting an ad network and want to white-label existing tech instead of building it yourself
2. You are having trouble scaling your ad network
3. You have an ad network and want to incorporate RTB traffic
4. You want to build a video ad server

When to think twice:

1. You are not an ad network
2. If you are price sensitive. For instance, for someone with 50MM monthly display impressions, it would be $2,500/month on EPOM, versus free on GAM (though GAM may not provide the features you want)

7. Broadstreet

Type: Hosted third-party ad server for digital magazines

Broadstreet provides a niche adserver to digital magazines and online news sites whose focus is on direct-sold ads.

G2Crowd: 4.9 stars

When to consider them:

1. You are a digital magazine / news site with a focus on direct-sales, not programmatic ads
2. You want to show sponsored content / promoted articles
3. You want an intuitive, simple ad server. Their pitch is they are DFP without the complexity

When to think twice:

1. You are not a digital magazine/news site
2. You want instant revenue via programmatic ads
3. You need a lot of platform customization
4. You want a server-side integration for faster ad calls

8. LiveIntent

Type: Hosted third-party ad server for emails

While most ad servers offer email compatibility, email-only ad servers exist too, such as LiveIntent. LiveIntent acts as both an ad server and a network for monetizing emails. They also offer robust filtering options to personalize and optimize messaging.

G2Crowd: 3.5 stars

When to consider them:

1. You are looking for email ad serving only
2. You want the ad server to provide ads for you
3. You want to use your data - such as website visiting behavior - in your targeting

When to think twice:

1. You want to fill the ad slots with direct-sold ads or internal promos only. LiveIntent requires you to use their programmatic demand, which can be frustrating to many brands who want to sell ads directly
2. You want an ad server that can show ads across desktop and mobile too

9. MoPub

Type: Hosted third-party ad server for mobile apps

Most ad servers enable app targeting, but if you're looking for an app-specific mobile ad delivery platform, MoPub will be a great option. Bought by Twitter in 2013, they're the leading mobile app mediation solution for managing direct-sold and programmatic ads.

G2Crowd: 3.5 stars

When to consider them:

1. You want to show ads just within your mobile app(s)
2. You want to manage ads across direct and programmatic sources
3. You want easy access to programmatic demand

When to think twice:

1. You also want to show ads on desktop, mobile web, or in emails
2. You want flexibility around business logic and targeting. For instance, MoPub does not enable behavioral targeting, day parting, page content targeting, or user agent targeting
3. You want to do server-side ad insertion instead of installing another SDK

10. Ad Inserter

Type: WordPress plug-in ad server

If you have a low-traffic WordPress site and GAM seems too complicated, the Ad Inserter WP Plug-in is a good option. It has the most active installations of any WP ad server solutions and provides an easy way to manage direct deals and Google AdSense ads.

When to consider them:

1. You built your site on WordPress
2. You don’t have much volume and expect to use Google AdSense to fill all impressions
3. You want an easy-to-install plug-in

When to think twice:

1. You want access to more demand than just AdSense
2. You want to have more control over business logic and targeting
3. You have more volume than 50K impressions/month

Can you summarize that for me?

Yup! Here's a quick highlight of which ad server is going to be best for you, based on your needs:

Where are you getting demand?	Need a customizable ad server?	Where are you showing ads?	How do you define yourself?	Your best bet is:
Direct + programmatic	Yes	Websites, apps, emails, DOOH, in-game	You want a fully-customized ad server without the hassle of building it from scratch	Kevel
Programmatic	No	Websites, apps	Standard web publisher	Google
Programmatic	No	Emails	Brand looking to monetize large email list	LiveIntent
Programmatic	No	Websites	Low-traffic WordPress site	Ad Inserter WP Plug-in
Programmatic	Yes	Websites, apps	An ad network, ad exchange, etc	EPOM
Programmatic + direct	No	Websites	You want a basic ad server, but don't want to build it or work with a vendor	Self-host with Revive
Programmatic + direct	No	Apps	An app developer who wants to manage direct sold and programmatic app ads	MoPub
Direct	No	Websites, apps	A digital magazine	Broadstreet

The long-tail third-party options

The above brands constitute over 90% of the market, and it’s highly recommended you work with a leader. But if the above options aren’t interesting, below are some additional third-party ad servers, most being smaller brands with fewer than 15 employees.

The benefits of a smaller company is that support tends to be better, but they usually come with fewer features and run the risk of going under, forcing you to migrate ad servers.

1. Standard Ad Servers - AdGlare, Adhese, AdPlugg, AdSpeed, AdSpirit, AdvertServe, Avid, iBillboard, InClick, Lite Ad Server, UpRival, Zedo
2. Self-Hosted Ad Servers - OIO, dJax, InOut
3. Email Ad Servers - Passendo, PowerInbox
4. WP Plug-In Ad Servers - Advanced Ads, AdRotate

The shuttered ad servers

Time has not been friendly to once-leading ad servers, so I wanted to point out some major ad servers that are no longer around. Indeed, if you were to look at a “Best Ad Server” blog from 2014, these would likely have been in the Top 5.

1. OpenX - In 2019, OpenX officially shuttered its ad serving arm to focus on video and programmatic. This was surprising to many, considering for a long time OpenX was the #2 ad server behind Google
2. AdTech (Verizon Media) - 2019 also saw AdTech get decommissioned. Their path was circuitous, providing infrastructure for ONE by AOL and then Verizon’s Oath platform
3. AppNexus's Open AdStream - 2019 saw yet another top ad server fall, with AppNexus’s Open AdStream shutting down so AppNexus could focus on programmatic
4. Atlas - Facebook acquired the Atlas ad server from Microsoft in 2013 but had trouble finding a use for it. It was shut down in 2016
5. Polymorph - Previously AdsNative, Polymorph was bought in 2019 by Walmart, who promptly shut down their commercial ad server

What are my next steps?

If you're still unsure of what to do next, we are more than happy to set up a 15-min consultation to walk through your needs and discuss the best path forward. We wish you the best in your quest to launch an ad server.