ads.txt + app-ads.txt: what they actually do

ads.txt is one of the most-misunderstood compliance signals in programmatic. Most publishers either copy a stranger's file or ignore it entirely. Here's what it actually does and how to set it up correctly.

What ads.txt is

ads.txt is a plain-text file you publish at the root of your domain (literally https://yoursite.com/ads.txt) that declares which sellers are authorised to monetise your inventory. It's an IAB standard from 2017.

The format is one line per authorised seller:

google.com, pub-1234567890123456, RESELLER, f08c47fec0942fa0

That line says four things:

• google.com— the SSP / exchange that's allowed to sell my inventory
• pub-1234567890123456 — my publisher account ID inside that SSP
• RESELLER — whether that account is selling DIRECT (their own deal) or as a RESELLER (passing demand through)
• f08c47fec0942fa0— Google's IAB-issued seller certification ID (always the same constant)

Why it matters

Ad-fraud detection systems (and SSPs themselves) check ads.txt before bidding on your inventory. If they don't see an authorised entry for the account claiming to sell, the bid is blocked. Missing entries = real revenue loss.

app-ads.txt for apps

Apps don't have a domain you control at root level, so the IAB defined app-ads.txt instead. You publish the file at the developer URL registered with the App Store / Play Store. Same format, same rules.

Crawlers check the "Website" field of your app listing → visit that domain's /app-ads.txt → confirm the authorised sellers match what the SDK is claiming.

What Adbris ships for you

Adbris publishes a centralised ads.txt at adbris.com/ads.txt that aggregates all our partners' pub-IDs. Publishers can either:

• Include the per-source entries we generate (one or two lines) in their own ads.txt
• Or redirect their /ads.txt to adbris.com/ads.txt via meta-redirect

Both satisfy Google's ads.txt validator. The dashboard's Policy Center has a per-source verifier that crawls your site and tells you which expected entries are missing.

The 30-second checklist

For websites

• File lives at /ads.txt at the apex domain (not www-prefixed unless that's your canonical)
• Plain text, Unix line endings, UTF-8
• One entry per line, no leading whitespace
• Comments start with #
• HTTP 200 — no 301 redirects, no behind-auth

For apps

• File lives at /app-ads.txt at the developer URL
• Developer URL must match the one in the App Store / Play Store listing
• Same format as ads.txt

Last note: don't over-include

Some publishers paste 200-line ads.txt files copied from larger sites. Don't. Only declare sellers who actually sell your inventory. Stale entries are noise the validators flag.