ads.txt and app-ads.txt explained: a quick check to see if an ad network is real
If you run ads on a website or app, you will sooner or later meet two small text files: ads.txt and app-ads.txt. They look technical, but they are one of the simplest ways to check whether an ad network is a real participant in the advertising ecosystem. This guide explains what they are, how to read them and what their absence can and cannot tell you.
What ads.txt and app-ads.txt are
They are public files, created by the IAB Tech Lab, in which a publisher lists the companies authorised to sell its inventory. Buyers use them to avoid paying unauthorised resellers. A website puts ads.txt at its root (for example, yourdomain.com/ads.txt); apps publish app-ads.txt on the developer website listed in the app store.
Each line contains the ad system's domain, your account ID there, the relationship (DIRECT or RESELLER) and, often, a certification authority ID.
Why this helps you check a network
- Established networks appear in many files. Search the network's domain across public ads.txt files or lookup tools. A real, active network typically appears on a large number of publishers.
- They publish clear instructions. A network that wants you to be paid correctly will tell you exactly which line to add and where.
- Their domain has a footprint. A company that exists only on its own marketing site and appears in no one else's file deserves an extra question.
How to check, step by step
- Ask the network for the exact line you need to add and what the relationship type is.
- Search the network's domain in a public ads.txt lookup tool and see how many publishers include it.
- Check a few well-known sites' ads.txt files (just add /ads.txt to the domain) to see whether the network appears there.
- Look for the network in industry directories, documentation and SDK repositories, not only on its own site.
- After you add the line, check that the network confirms receipt and that your account ID appears in its dashboard.
What ads.txt cannot tell you
- It does not prove they will pay you. A network can be technically correct and still pay late or not at all.
- Absence is not proof of fraud. New or niche networks may be small. Treat it as one signal among many.
- Presence is not a certificate. Anyone can add a line. Combine this check with company verification and references from paid publishers.
Frequently asked questions
Do I need ads.txt if I only use one network? It is still recommended: it protects your inventory from unauthorised resellers.
Does a missing file mean I will not be paid? No. It means one of the usual signals of a mature network is missing; look at the others.
The bottom line
Ads.txt is a ten-minute check that tells you whether a network lives in the real ecosystem. It does not replace checking the legal entity, the payment terms and references from publishers who have actually been paid.
This article is general preventive information written by a group of affected people. It is not legal or financial advice. References to UndrAds reflect the opinion and testimony of the affected parties about alleged facts.