DollarWise

Free ads.txt Validator — Check Your File Against the IAB Spec

October 19, 2026 · 2 min read · By the DollarWise team

A malformed ads.txt can silently block ad revenue. Paste your ads.txt content or upload the file, and this tool validates every line against the IAB spec — record format, DIRECT/RESELLER relationships, missing fields, and duplicate seller entries — with line numbers and a downloadable report.

ads.txt Validator

Validate every line of your ads.txt against the IAB spec — errors with line numbers.

100% Free Forever No Sign-up No Credit Card Private — files never leave your browser Unlimited Use

1 Add your ads.txt

…or upload the file instead:

2 Check options

Flag duplicate seller entries
Same domain + publisher ID listed twice is almost always a copy-paste error.
Warn if no DIRECT entries
Most publishers should have at least one DIRECT relationship (e.g. Google AdSense).
Require certification authority ID
The 4th field (e.g. f08c47fec0942fa0 for Google). Optional per spec, but good hygiene.

3 Validate & report

Working…

Validation report

🎉 Free forever. No sign-up. No credit card. No limits.

Validate as many ads.txt files as you like — everything runs in your browser.

How it works

The IAB ads.txt spec is simple: each data line is domain, publisher_id, DIRECT|RESELLER[, certification_id], comments start with #, and variable declarations (CONTACT=, SUBDOMAIN=, OWNERDOMAIN=, MANAGERDOMAIN=) are allowed. This tool checks every line in your browser: at least 3 comma-separated fields, a syntactically valid domain, a non-empty publisher ID, and a relationship of exactly DIRECT or RESELLER (case-insensitive). Optional checks flag duplicate domain+ID pairs, missing certification IDs, and files with zero DIRECT entries. The downloadable report lists the verdict for every line.

Honest limitation: syntax is only half the story — this tool can’t verify that the publisher IDs actually belong to you or that the file is live at yoursite.com/ads.txt. After fixing syntax, confirm the live file loads and matches what you validated here.

Everyday uses

  • AdSense/Ad Manager publishers — verify your ads.txt before and after every edit; one typo can pause revenue.
  • New sites — generate your first ads.txt, then validate it here before going live.
  • Agencies — audit client files in bulk without touching their servers.
  • Reseller cleanup — spot duplicate entries added by multiple ad partners over time.
  • Revenue troubleshooting — “ads.txt missing/invalid” warnings in AdSense often trace to a single bad line.