An ad server (also written adserver) is software that decides which ad to show in an ad space, delivers it to the visitor's browser or app, and records what happens next: impressions, clicks and conversions. Publishers use ad servers to fill their websites and apps with ads, advertisers use them to run and measure campaigns, and ad networks use them to connect the two. This guide explains how an ad server works, the different types, and what to look for when you choose one.
What is an ad server?
An ad server is the decision engine behind online advertising. Every time a page with an ad space loads, the ad server receives a request, looks at everything it knows about that request (country, device, browser, language, the website and placement, the time of day), checks which campaigns are allowed to show there, picks the best one and sends it back. All of that happens in a few milliseconds, millions or billions of times a day.
Besides choosing ads, an ad server:
- Stores the creatives: banners, videos, native ads, text links and push notifications.
- Applies the campaign rules: targeting, budgets, schedules and frequency caps (how often one visitor may see the same ad).
- Counts everything: impressions, clicks, conversions, revenue and cost, so advertisers know what they paid for and publishers know what they earned.
- Optimises: rotates creatives and landing pages, and moves traffic to whatever performs best.
The first ad servers appeared in the mid-1990s, when websites needed a way to swap banners without editing their pages. Today the same idea runs display, video, mobile, native, push and even search ads, and it is connected to real-time bidding (RTB) marketplaces.
How does an ad server work?
From the moment a visitor opens a page to the moment the ad appears, an ad server goes through the same steps:
- The ad request. The page contains an ad tag: a small piece of code the publisher placed in an ad zone. When the page loads, the tag calls the ad server.
- Reading the request. The ad server identifies the ad zone, the website and the visitor's context: country and region, device, operating system, browser, language, connection type and time.
- Finding eligible campaigns. It filters every active campaign down to the ones allowed in this zone: right format and size, matching targeting, budget left, schedule active and frequency cap not reached.
- Choosing the winner. The remaining ads compete. Depending on the setup the winner is the highest effective price (eCPM), a guaranteed direct deal that must deliver, or the best bid from an RTB auction with outside buyers.
- Delivering the ad. The ad server returns the creative (an image, video, native layout or redirect), and the browser or app renders it.
- Tracking. The impression is counted when the ad is shown, the click when it is clicked, and the conversion when the advertiser reports a sale or sign-up through a postback.
- Reporting and billing. All events flow into statistics, so advertisers are charged and publishers are paid on the same numbers.
A good ad server does all of this in a fraction of the page's load time. GoAdserver, for example, makes its decision in under one millisecond.
Types of ad servers
First-party (publisher) ad servers
A first-party ad server is run by, or for, the publisher: the owner of the website or app. It manages the publisher's own ad zones, decides which campaign fills each impression (direct deals, house ads, ad networks or RTB demand) and reports what every zone earns. The large advertising platforms each offer one to publishers, usually tied closely to their own demand.
Third-party (advertiser) ad servers
A third-party ad server works for the advertiser or agency. It hosts the creatives, serves them into many different publishers' sites and counts impressions and clicks independently, so the advertiser can check every publisher's numbers and compare them in one place. Agencies and larger brands use them to keep one set of numbers across every site a campaign runs on.
Ad network ad servers
An ad network sits in the middle: it signs up advertisers and publishers and needs both sides in one system. Its ad server lets advertisers create and fund campaigns, lets publishers create ad zones and get paid, and gives the network operator control over pricing, approval, traffic quality and payouts. This is the kind of ad server you need to start your own ad network.
Hosted (SaaS) and self-hosted ad servers
A self-hosted ad server is software you install and run on your own servers, often an open-source package. You control everything, but you also handle scaling, updates and security. A hosted or SaaS ad server runs in the provider's cloud: you log in to a panel and the provider keeps it fast and available. Most businesses choose hosted today, because ad traffic arrives in large peaks and a slow ad server costs money on every request.
White-label ad servers
A white-label ad server is a hosted ad server that carries your brand instead of the provider's: your logo, your colours and your own domains for the control panel and the ad tags. Your advertisers and publishers only see your company. It is the fastest way to launch an ad network or a branded ad platform without building the technology yourself.
Ad servers by ad format
Most modern ad servers handle several formats; some specialise.
- Display and banner ad servers serve image, HTML5 and iframe banners in standard sizes.
- Video ad servers deliver pre-, mid- and post-roll ads to video players, usually through VAST, the standard tag that video players understand. They also serve in-page video, sliders and outstream units for sites without a player.
- Mobile ad servers serve mobile websites and apps, with targeting by device, operating system and connection type, and formats that fit small screens such as interstitials and portrait video.
- Native ad servers render ads in the look of the surrounding content: recommendation widgets, in-feed units and native bars.
- Push, pop and redirect ad servers handle the high-volume performance formats: push notifications, pop-unders, new tabs, direct links and smartlinks.
- Email ad servers monetise the links and banners in newsletters, where no JavaScript can run.
- Retail media ad servers show sponsored products and banners on online shops and marketplaces, usually built from the shop's product feed, and report sales back to the brands that pay for them.
GoAdserver supports more than 35 ad zone types across all of these. See the full list on our ad formats page.
Ad server vs ad network vs SSP vs DSP
These terms are often mixed up. The short version:
| Term | What it is | Who uses it |
|---|---|---|
| Ad server | The technology that stores ads, decides which one to show and counts the results. | Publishers, advertisers, ad networks |
| Ad network | A business that buys ad space from many publishers and sells it to advertisers. It runs on an ad server. | Advertisers looking for traffic, publishers looking for buyers |
| SSP (supply-side platform) | Sells a publisher's impressions to many buyers at once through real-time bidding. | Publishers and ad networks with inventory |
| DSP (demand-side platform) | Buys impressions in real time across many SSPs and exchanges for advertisers. | Advertisers, agencies, media buyers |
Modern platforms combine these roles. GoAdserver is an ad server that can also act as an SSP (selling your inventory to outside buyers over OpenRTB) and as a DSP (bidding on other exchanges' traffic for your advertisers). Read more about RTB in GoAdserver.
Key features to look for in an ad server
- Speed and scale. Every millisecond counts, and traffic peaks are sudden. Ask how fast the ad decision is and how many requests per second the platform handles.
- Targeting. Country and region, device, operating system, browser, language, connection type, ISP, time of day, content category and retargeting audiences.
- Campaign controls. Budgets and pacing, schedules, frequency capping, bid adjustments per country or placement, and approval of creatives.
- Pricing models. CPM, CPC and CPA campaigns, flat-rate and direct deals, and real-time bidding next to each other.
- Optimisation. Automatic rotation of creatives and landing pages, and rules that pause or block placements that don't perform.
- Traffic quality. Bot and fraud filtering on every request, so nobody pays for traffic that isn't human.
- Reporting. Real-time statistics you can break down by campaign, zone, country, device and time, plus conversion tracking with postbacks.
- Ad formats. The formats your publishers and advertisers actually use, including video and mobile.
- API and integrations. An API for everything in the panel, so you can automate campaigns, reporting and billing.
- Branding. If you run a network for clients, a white-label panel on your own domain.
Examples of ad servers
Most ad servers on the market fall into a few families. Which one fits depends on who you are and how much control you want:
- Publisher ad servers built into large ad platforms: easy to start with and often free at low volume, but closely tied to the platform's own exchange and demand, so the platform has a big say in what fills your ad space.
- Advertiser-side (third-party) ad servers: used by agencies and brands to host their creatives, serve them across many publishers and count every impression and click independently.
- Open-source, self-hosted ad servers: free to download and fully under your control, but you run the servers, scaling, updates and security yourself.
- API-first ad servers: hosted decision engines that developers build their own ad products on, with more coding work and a lighter control panel.
- Hosted white-label ad servers such as GoAdserver: a complete platform under your own brand for ad networks, ad managers, publishers and offer networks, with RTB, tracking and automated media buying.
How to choose an ad server
Start with what you are building:
- Monetising your own sites? You need a publisher ad server with good fill from several demand sources and clear earnings per zone. See ad management.
- Running campaigns on many sites? You need independent counting, conversion tracking and cost data. See the tracker.
- Starting an ad network? You need both sides in one platform, under your own brand, with billing and traffic quality handled. See the white-label ad network.
- Running affiliate offers? You need offer management, smartlinks and postbacks. See the offer network.
Then compare speed, formats, targeting, reporting and the total cost at your traffic volume, not just the starting price.
GoAdserver: a white-label ad server for your business
GoAdserver is a hosted ad server you can run under your own brand. One platform covers an ad network, an ad manager for your own and bought traffic, an offer network and a tracker. It serves more than 35 ad formats, makes its ad decision in under a millisecond, connects to RTB buyers and sellers, filters bot traffic, and gives advertisers, publishers and your own team real-time statistics and a full API. Compare the features and pricing, or talk with our team.
Frequently asked questions
What does an ad server do?
It stores ads, decides which ad to show for each ad request based on targeting and price, delivers it, and counts impressions, clicks and conversions for reporting and billing.
Is an ad exchange the same as an ad server?
No. An ad exchange is a marketplace where impressions are auctioned to many buyers in real time; an ad server decides which ad fills each impression and counts the results. Large ad platforms often sell a publisher ad server together with their own exchange, which is why the two get mixed up.
What is the difference between a first-party and a third-party ad server?
A first-party ad server works for the publisher and decides what fills its ad space. A third-party ad server works for the advertiser and serves and counts its ads across many publishers.
What is a video ad server?
An ad server that delivers video ads, usually to a video player through a VAST tag, or as in-page and slider video on sites without a player.
Do I need an ad server if I work with an ad network?
Not to get started, because the network's ad server does the work. Once you sell to several networks or direct advertisers, your own ad server lets you decide who fills each impression and see what every placement really earns.
What is a hosted ad server?
An ad server that runs in the provider's cloud instead of on your own servers. You manage campaigns in a web panel; the provider handles speed, scaling and updates.
How much does an ad server cost?
Hosted ad servers usually charge a monthly fee, a price per thousand impressions, or both. Self-hosted software can be free to download, but you pay for the servers and the people who run them. See GoAdserver's pricing.