ads.txt Validator
Paste your ads.txt or fetch one live by URL, check it against the IAB spec (1.0.3 + 1.1),
and cross-reference every seat against the ad systems' sellers.json — the same supply-chain
checks used in real publisher audits, plus a 0–100 Authorization Health score. Pasting stays in your
browser; only live URL and sellers.json lookups go through our server (the browser can't fetch them).
What ads.txt is, and what this validator checks
ads.txt (Authorized Digital Sellers) is a plain-text file published at the root of a domain — example.com/ads.txt — that lists every advertising system and account ID the publisher has authorized to sell its inventory. Buyers and SSPs read it to confirm an impression is coming from a legitimate, authorized seller and to shut out counterfeit inventory.
The format is strict, and the file is usually maintained by pasting in blocks of lines from each ad partner. That is exactly how problems creep in: duplicate records, the wrong relationship, a partner left in long after it stopped selling, or a missing ownership declaration. This validator checks the file against the IAB spec and the same hygiene checks used in real publisher audits — all in your browser, with nothing uploaded.
What this validator checks
- Record format — three required fields (advertising system, publisher account ID, relationship) plus the optional certification authority ID
- Relationship is DIRECT or RESELLER, and conventionally uppercase
- Duplicate records (each line must be unique) and DIRECT/RESELLER contradictions for the same seat
- OWNERDOMAIN declared once, and MANAGERDOMAIN scoped correctly (one default, additional ones country-coded) — ads.txt 1.1
- INVENTORYPARTNERDOMAIN, CONTACT and SUBDOMAIN directives
- Lowercase domains, stray tabs and whitespace, and BOM / CRLF hygiene
- sellers.json cross-reference — confirms each seat is listed by the ad system, and flags non-existing seats, confidential sellers, and DIRECT/RESELLER vs
seller_typemismatches - For fetched files — HTTP status, wrong content type, and cross-domain redirects
It also fetches a live file by URL, scores Authorization Health out of 100, compares two versions, checks a block of required lines, and supports app-ads.txt — with one-click fixes and a cleaned download.
Frequently asked questions
What is ads.txt?
ads.txt (Authorized Digital Sellers) is a public text file at /ads.txt that lists the advertising systems and account IDs a publisher has authorized to sell its inventory. Buyers read it to avoid counterfeit or unauthorized inventory.
Why should I validate my ads.txt?
A single malformed line, duplicate record, or wrong relationship can drop an authorization or confuse buyers, which costs revenue. Validation catches those issues before they go live.
What is the difference between DIRECT and RESELLER?
DIRECT means you control the account at that advertising system. RESELLER means a partner you authorized controls the account and resells your inventory on your behalf.
What are ownerdomain and managerdomain?
They were added in ads.txt 1.1. OWNERDOMAIN declares the business that owns the inventory; MANAGERDOMAIN declares the primary partner that monetizes it. Both help buyers verify the supply path back to the real owner.
Does this tool upload or store my file?
Pasted or uploaded files never leave your browser, so you can safely check an unreleased file. If you fetch a live file by URL or run the sellers.json check, only that URL or domain goes through our server — never your pasted content. Nothing is stored either way.
How often should I re-check my ads.txt?
Re-validate whenever you add or remove a partner, and on a regular schedule. Vendors often hand you blocks of lines to paste in, which is how duplicates and contradictions creep in over time.
Which ads.txt version does this follow?
Both. IAB ads.txt 1.0.3 (2021) for the record format and certification authority field, and 1.1 (2022) for the OWNERDOMAIN and MANAGERDOMAIN variables.
Can it fetch my live ads.txt by URL?
Yes. Enter a domain or URL and the validator fetches the live file server-side, because the browser's CORS policy blocks fetching it directly. It follows redirects and flags problems like a domain returning HTML instead of a real ads.txt, or redirecting to a different domain. The validation itself still runs in your browser.
What is the sellers.json cross-reference?
After validating, you can cross-reference the file against each ad system's sellers.json. For every record the tool confirms your account ID is actually listed by that system, and flags seats that don't exist, sellers marked confidential, and DIRECT/RESELLER relationships that disagree with the seller_type. It's the supply-chain check most free validators skip.
Can I compare two ads.txt files or check for required lines?
Yes. Compare mode diffs two versions and shows which sellers were added or dropped. Required-lines mode takes a block of lines a partner asked you to add and reports each as present, missing, or malformed — useful before a change goes live. app-ads.txt is supported with the same checks.