When you open a free game and a banner appears, something remarkable has happened in the blink of an eye. Dozens of companies may have competed for the right to show you that ad, with prices set by an automated auction. Platforms like MoPub were part of the plumbing that made this possible, and understanding the basics reveals how free apps make money.
The cast of characters
Mobile advertising has many acronyms, but the roles are straightforward.
- Publisher: the app developer with ad space to sell.
- Advertiser: a company wanting to reach users, such as a game studio promoting its next release.
- Ad network: a company that aggregates advertisers and sells their ads across many apps.
- Supply-side platform (SSP): software that helps publishers sell their ad space to the highest bidder. Ad exchanges and monetization platforms often fit here.
- Demand-side platform (DSP): software that helps advertisers buy space across many publishers efficiently.
- Ad exchange: a marketplace where supply and demand meet for automated auctions.
What happens in a fraction of a second
Here’s a simplified version of a real-time bidding auction.
- You open an app with an ad slot.
- The app sends an ad request, including details like device type, general location, app category, and sometimes an advertising identifier.
- The exchange broadcasts a bid request to demand platforms.
- Advertisers’ systems evaluate the request and decide if it matches their targeting and how much to bid.
- Bids return within roughly a hundred milliseconds.
- The highest bid wins, and the winning ad is delivered to the app.
- The app displays it, and tracking records impressions, clicks, or installs.
The entire process happens before the screen finishes loading.
Mediation: choosing among many sources
Publishers often work with several networks, so they use mediation software that decides which source gets each ad request. A waterfall approach asks networks in order, starting with the highest historical price. A more modern approach, often called header bidding or unified auctions, lets all sources bid at once, so the best price wins on each impression. This tends to raise revenue for publishers because it reduces leaving money on the table.
How money flows
Advertisers pay in several ways:
- CPM: a price per thousand impressions.
- CPC: a price per click.
- CPI: a price per app install.
Intermediaries take a fee at each step, so only part of the advertiser’s spend reaches the publisher. This is a long-standing criticism of ad tech: complex chains can obscure where money goes. Transparency initiatives and standardized files, like those that let publishers declare authorized sellers, aim to reduce fraud and clarify the chain.
Privacy changes upended the system
Targeting depended heavily on device advertising identifiers. When mobile operating systems introduced prompts asking users to allow tracking, many people said no, and the data available for targeting shrank. Advertisers had to rely more on context, such as app type or content, and on aggregated measurement. Smaller players without strong first-party data were hit hardest.
The result accelerated consolidation. Companies with large scale and their own audience data gained advantage, and some mid-sized ad tech businesses were sold or merged. That’s one reason you see acquisitions in this sector: buyers want inventory, technology, and publisher relationships.
Tips for app developers
- Test multiple ad networks and formats; revenue can vary a lot.
- Balance ad frequency against user experience. Too many ads drive people away.
- Use rewarded ads, where players choose to watch for in-game benefits. They typically earn well and annoy users less.
- Pay attention to load time and app size, since heavy ad software affects performance.
- Follow privacy rules and be transparent about data use.
What this means for users
Ads fund countless free apps, and the targeting behind them depends on data. You can limit tracking through system settings, reset your advertising identifier, or pay to remove ads from apps you use often. Each choice trades money, convenience, and privacy differently.
Takeaway
Mobile ad exchanges are the invisible auction houses of the app economy. They connect millions of apps and advertisers, setting prices in milliseconds. Understanding them clarifies why apps show the ads they do, why privacy rules have reshaped the business, and why ad tech companies keep merging and changing hands.
Featured image: Astrologer ads in KSRTC bus.jpg by Mallikarjunasj, CC BY-SA 4.0, via Wikimedia Commons.
