The ads.txt (Authorized Digital Sellers) standard was introduced by the IAB Tech Lab to combat ad fraud by letting publishers declare which companies are authorized to sell their inventory. It's a simple text file at your domain's root, but getting it wrong can cost you real money.
Why ads.txt Errors Matter
When a buyer's DSP checks your ads.txt and doesn't find the seller they're trying to buy from, the bid is dropped. When there are syntax errors, some DSPs may ignore your entire file. Either way, you lose demand, and revenue.
The Most Common Errors We Find
1. Syntax Errors (Found in 28% of Sites)
The ads.txt format is strict: each line must follow the pattern domain, publisher-id, relationship-type [, certification-authority-id]. We frequently find lines with extra spaces, missing commas, invalid relationship types (like "RESELLER #comment" where the comment isn't properly separated), and non-ASCII characters.
In one recent audit of moneycontrol.com, we found 14 syntax errors including invalid relationship values like "RESELLER #APL" and "DIRECT #Biddigi". The hash comment was merged into the relationship field.
2. Duplicate Entries (Found in 35% of Sites)
Over time, as publishers add new demand partners or different team members edit the file, duplicate entries accumulate. While duplicates don't directly block revenue, they make the file harder to maintain and can mask other issues. We've seen files with 17+ duplicate entries.
3. Unrecognized Seller Domains (Found in 40% of Sites)
This is the biggest silent revenue killer. Publishers often have entries for seller domains that are misspelled, have changed names, or simply don't exist. DSPs can't validate these entries, so the corresponding demand is lost. In our moneycontrol.com audit, we found 408 entries with unrecognized domains.
4. Missing Key Partners
The flip side of unrecognized domains: sometimes publishers forget to add entries for their actual demand partners. If you've recently added a new SSP or exchange but haven't updated ads.txt, their bids will be filtered.
How to Fix Your ads.txt
First, run a RevenueRx audit to get a complete syntax check, duplicate detection, and partner authorization analysis. Then: remove all syntax errors, deduplicate entries, verify every domain against the IAB's official list, and ensure all your active demand partners are listed. Set a monthly reminder to review the file whenever you change demand partners.