What Is Open Bidding? A Beginner's Guide for App Publishers

The mobile app industry has become one of the fastest-growing digital markets in the world. Every day, millions of people use apps to shop, learn, play games, create content, stream videos, and connect with others. For many developers, advertising has become one of the most important ways to generate revenue while keeping apps free for users.

But earning the highest possible advertising revenue isn't as simple as displaying ads. The key is creating competition among advertisers so every ad impression has the opportunity to earn its maximum value.

That's where Open Bidding comes in.

Whether you're an independent developer launching your first app or an established publisher looking to improve monetization, understanding Open Bidding can help you make smarter decisions about your advertising strategy.

What Is Open Bidding?

Open Bidding is a programmatic advertising technology that allows multiple advertising networks and demand partners to compete for every available ad impression in real time.

Instead of relying on a single advertising network, Open Bidding creates an auction where several buyers bid simultaneously.

The highest eligible bidder wins the opportunity to display their advertisement.

This increased competition often leads to:

• Higher advertising revenue

• Better fill rates

• Improved eCPMs

• More efficient monetization

For publishers, Open Bidding helps maximize the value of every impression without manually managing multiple waterfalls.

How Traditional Ad Waterfalls Work

Before Open Bidding became popular, most mobile apps used a waterfall system.

In a waterfall setup:

1. The app requests an advertisement.

2. The first advertising network receives the request.

3. If it cannot fill the request, the opportunity moves to the next network.

4. The process continues until an ad is served.

While simple, this system has several disadvantages.

A higher-paying advertiser lower in the waterfall may never receive the opportunity to bid because another network already filled the request.

This can leave money on the table.

How Open Bidding Works

Open Bidding changes the process entirely.

Instead of asking networks one at a time, multiple demand sources receive the request simultaneously.

Each advertiser submits a bid based on:

• User location

• Device type

• App category

• Audience characteristics

• Historical performance

• Campaign goals

The highest qualified bid wins almost instantly, and the winning advertisement appears in the app.

The entire process usually takes only milliseconds.

Why Competition Matters

Think of selling artwork at an auction.

If only one person is interested, you'll likely receive one offer.

If twenty collectors compete for the same piece, the final selling price often increases.

Open Bidding works in much the same way.

Every advertising network competes to purchase your inventory.

More competition generally leads to better pricing.

Benefits of Open Bidding

Higher Revenue

One of the biggest advantages is increased revenue.

When advertisers compete simultaneously, publishers often see improved eCPMs because every impression is auctioned fairly.

Better Fill Rates

Fill rate measures how often an ad request results in an advertisement being displayed.

By connecting multiple demand sources, publishers reduce the chances of empty ad spaces.

Higher fill rates create more earning opportunities.

Simplified Management

Traditional waterfalls require constant optimization.

Publishers frequently adjust network priorities and eCPM floors manually.

Open Bidding automates much of this process by allowing real-time competition.

Fair Auctions

Every eligible advertiser has the opportunity to bid.

Instead of giving preference based on waterfall position, Open Bidding rewards the highest-value advertiser.

Understanding eCPM

One of the most important advertising metrics is eCPM, or Effective Cost Per Mille.

"Mille" means one thousand.

eCPM measures how much revenue you earn for every 1,000 ad impressions.

For example:

• 1,000 impressions

• $15 revenue

Your eCPM equals:

$15.00

Increasing eCPM means earning more money from the same amount of traffic.

Open Bidding helps improve eCPM by encouraging stronger competition among advertisers.

Fill Rate Explained

Another key metric is fill rate.

Fill rate represents the percentage of ad requests successfully filled by advertisers.

For example:

• 10,000 requests

• 9,500 ads served

Your fill rate would be:

95%

A higher fill rate generally means fewer missed revenue opportunities.

What Is an Ad Impression?

An impression occurs every time an advertisement is displayed to a user.

More impressions usually create greater earning potential.

However, quality matters just as much as quantity.

High-quality users from valuable advertising markets often generate higher eCPMs than low-value traffic.

Geographic Performance

Advertising revenue varies significantly by country.

Markets such as:

• United States

• Canada

• United Kingdom

• Australia

• Germany

often generate higher eCPMs because advertisers spend more.

Growing digital markets including:

• India

• Brazil

• Indonesia

• Mexico

• South Africa

may produce lower average eCPMs but can generate substantial revenue through large audiences and rapidly increasing advertiser demand.

Successful publishers understand both traffic quality and geographic diversity.

What Is app-ads.txt?

Another important component of mobile advertising is app-ads.txt.

Developed by the Interactive Advertising Bureau (IAB), app-ads.txt helps prevent advertising fraud.

It allows publishers to publicly list which advertising companies are authorized to sell their inventory.

Benefits include:

• Increased advertiser trust

• Reduced fraud

• Better transparency

• Improved demand quality

Most major advertising platforms recommend or require publishers to maintain an accurate app-ads.txt file.

Common Open Bidding Partners

Many companies participate in Open Bidding ecosystems.

Examples include:

• Google

• AppLovin

• PubMatic

• InMobi

• Magnite

• Index Exchange

• OpenX

• Sharethrough

• Chocolate Platform

• MediaGrid

Each partner brings different advertiser relationships and strengths.

Adding reputable demand partners can increase competition and improve monetization opportunities.

Best Practices

If you're considering Open Bidding, follow these best practices:

Focus on User Experience

Advertising should never overwhelm users.

Poorly placed ads can reduce retention and hurt app ratings.

Grow Your Audience Organically

The best monetization strategy starts with real users.

Create valuable content, improve your app, and encourage positive reviews rather than relying on artificial traffic.

Monitor Key Metrics

Track:

• Daily active users (DAU)

• Monthly active users (MAU)

• eCPM

• Fill rate

• Impressions

• Ad requests

• Retention

• Session length

Understanding these metrics helps identify opportunities for improvement.

Update app-ads.txt

Whenever you add or remove advertising partners, ensure your app-ads.txt file remains current.

An outdated file may reduce advertiser confidence and limit demand.

The Future of App Monetization

Artificial intelligence, machine learning, and real-time bidding continue to improve digital advertising.

Future Open Bidding systems will become even more efficient by using predictive algorithms to determine which advertisers are most likely to deliver value for both publishers and users.

Privacy-focused advertising, contextual targeting, and first-party data strategies will also shape the future of mobile monetization.

Publishers who stay informed and embrace these technologies will be better positioned to grow sustainable revenue.

Final Thoughts

Open Bidding has transformed the way mobile app publishers monetize their inventory. By replacing traditional waterfall methods with real-time competition, it creates a fairer marketplace where every ad impression has the opportunity to earn its highest value.

For independent developers and growing businesses, Open Bidding offers a practical path to improving revenue without sacrificing user experience. Combined with high-quality content, an engaged audience, and a properly maintained app-ads.txt file, it can become an important part of a long-term monetization strategy.

As the mobile advertising ecosystem continues to evolve, publishers who understand concepts like Open Bidding, eCPM, fill rate, and programmatic advertising will be better equipped to maximize their app's earning potential while delivering value to users.

In today's competitive app economy, success isn't just about acquiring more users—it's about making every impression count. And with Open Bidding, every impression becomes an opportunity to create more value for advertisers, publishers, and users alike.