What Is Programmatic Advertising? A Publisher's Guide

What is programmatic advertising?

Programmatic advertising is the automated buying and selling of ad impressions by software instead of by people sending insertion orders and spreadsheets. When a page or app has an ad slot to fill, software on the publisher’s side describes that slot, software on the advertiser’s side decides whether it is worth buying and at what price, and the ad is chosen and shown in a fraction of a second. Most of it runs on real-time auctions, but fixed-price deals between one buyer and one seller can be programmatic too.

This guide is the overview. The two platforms at either end have their own page, DSP vs SSP, and the marketplace in the middle is covered in What is an ad exchange?. Here you will find how the pieces fit, the deal types, the transparency files, and what programmatic means for you as a publisher.

How programmatic advertising works

A single programmatic impression usually goes through these steps:

1. A user opens a page or an app screen. The page’s ad tag or the app’s SDK asks the publisher’s ad server or supply-side platform for an ad.
2. The sell side builds a bid request. It describes the slot (size, format, position), the site or app, the device, a rough location, any IDs the user’s consent allows, a price floor and a deadline.
3. Buyers evaluate it. Demand-side platforms check the impression against their advertisers’ campaigns and either bid with a price and an ad or pass.
4. The auction or deal decides. The highest qualifying bid wins, unless a deal gives a specific buyer priority.
5. The ad shows and is counted. Impressions are logged, invalid traffic is filtered, the advertiser is billed and the publisher is paid its share, usually on a CPM basis. What is CPM? explains that pricing.

Most of this traffic speaks one shared protocol, OpenRTB. IAB Tech Lab’s OpenRTB page describes real-time bidding as a way of trading media “that allows an individual ad impression to be put up for bid in real-time”, and lists OpenRTB 2.6 and 3.0 as the current specifications (checked on November 4, 2026). Because every exchange uses the same fields, one DSP can read bid requests from hundreds of sources.

The programmatic supply chain, from advertiser to publisher

Between the brand that pays and the site that shows the ad, several companies each do one job. One company often runs several of these roles, which is why the labels blur.

Data providers, verification vendors and fraud filters plug into this chain too. Each link takes a share of the money, which is why programmatic fees are a regular topic; DSP vs SSP covers the best-known study of where advertiser spend goes. Today most SSPs run their own exchange, so “SSP” and “exchange” are often the same company.

Older ad networks still exist next to this chain. A network buys or collects inventory and resells it, often programmatically itself. What is an ad network? explains the difference.

RTB, private marketplaces and programmatic guaranteed

Programmatic is not one marketplace. The same pipes carry four kinds of deals, and they differ in who may buy, how the price is set, and whether volume is promised.

Open auction (RTB)

Any approved buyer may bid on the impression, and the highest bid above the floor wins. This is what most people mean by real-time bidding. It gives you the widest demand and the least control over who buys.

Private marketplace (PMP)

A private marketplace limits the auction to invited buyers. Google’s Ad Manager help page on Private Marketplace deals calls them “non-guaranteed programmatic deals” and splits them into two types: Private Auctions, which are invitation-only auctions with a floor price, and Preferred Deals, which are fixed-CPM deals where one buyer gets the first chance to bid. In OpenRTB, a deal travels in the bid request as a deal ID, and a private_auction flag tells buyers whether only deal bids are accepted.

Programmatic guaranteed

Programmatic guaranteed is a direct deal run through programmatic pipes: one buyer, a fixed price and a reserved quantity. Google’s comparison of Programmatic Guaranteed and Preferred Deals says that in a guaranteed deal “inventory is designated only for that buyer at that price”, while in a Preferred Deal the inventory is not reserved and “buyers aren’t required to buy the inventory” (checked on November 4, 2026).

Small publishers mostly sell through the open auction. Private deals need buyers who know your site by name, which usually means a large or very specialized audience.

ads.txt, app-ads.txt and sellers.json

Because an impression can pass through several resellers before a buyer sees it, someone could claim to sell your inventory without your permission. IAB Tech Lab built three public files so buyers can check every seller.

• ads.txt stands for Authorized Digital Sellers. You place it at the root of your domain and list each company allowed to sell your inventory, with your account ID at each one and whether the account is DIRECT (you control it) or RESELLER (someone else sells it for you). IAB Tech Lab’s ads.txt page dates version 1.0 to June 2017 and lists version 1.1 from August 2022 as the current one.
• app-ads.txt is the same idea for apps distributed through app stores and connected TV stores. The file lives on the developer website listed in your store page.
• sellers.json is published by SSPs and exchanges. According to IAB Tech Lab’s sellers.json page, it lets buyers identify the “direct sellers of or intermediaries in the selling of digital advertising”, and it works with the SupplyChain object (schain) in each bid request, which lists every company that touched that request. The OpenRTB working group finalized both on July 31, 2019.

Google’s Ad Manager help page on ads.txt says using the file “is not mandatory, but is highly recommended”, because it helps protect you from counterfeit inventory. In practice, many buyers skip impressions from sellers that are not listed, so a missing or outdated file shows up as lower fill.

Pros and cons of programmatic for publishers

What you gain

• Demand without a sales team. Thousands of buyers can bid on your impressions through a few integrations.
• Price discovery per impression. Each impression is priced on its own, so a valuable visitor can earn more than your average.
• High fill. With enough buyers, most of your slots get an ad. What is fill rate? explains why that matters as much as price.
• Flexibility. You can sell your best placements through private deals and let the open auction take the rest.

What it costs you

• Fees along the chain. Every intermediary takes a share before the money reaches you.
• Less control over ads. Blocking categories and advertisers helps, but you will not approve every creative by hand.
• Page weight and speed. More partners mean more scripts and requests. What is header bidding? covers how to keep that in check.
• Volatile earnings. Prices change with seasons, budgets and audience. Estimated earnings can also fall after invalid traffic is removed.
• Traffic quality rules. Buyers filter bots, and incentivizing users to view or click ordinary ads is not allowed. Ad fraud and bot traffic lists the warning signs.

How a publisher gets access to programmatic demand

You rarely connect to exchanges one by one. The usual routes are:

• An ad network or managed partner that already plugs into programmatic demand and handles setup for you.
• A publisher ad server plus SSPs, often with header bidding on websites so several SSPs bid at once.
• Mediation and in-app bidding for mobile apps. In-app bidding vs waterfall and What is ad mediation? explain the app side.

Whichever route you take, keep your ads.txt or app-ads.txt current, reserve space for every ad slot so pages do not jump, and judge partners on revenue per 1,000 requests, not on the highest CPM in their pitch. Best ad networks for publishers compares common starting points.

Where an offerwall fits next to programmatic

An offerwall is not programmatic. No impression is auctioned, no DSP bids, and no bid request goes out. Advertisers agree a payout for a completed action, such as installing a game and reaching a level or finishing a survey, and your users choose offers to earn your site’s or app’s own currency. You earn when the advertiser confirms the action. That makes it a pay-per-result format that sits beside your ad slots and does not compete with them for the same impression. It fits sites, apps, games and communities with logged-in users who collect points or coins. It does not replace display ads on a site whose visitors are anonymous, one-time readers. What is an offerwall? explains the model.

Frequently asked questions