Ad tag checker and live preview
Ad tag checker: test and preview an ad tag before it goes live
Paste a third-party ad tag and check it in your browser: markup, HTTPS, macros, size and click tracking, then run it live in a sandboxed slot. The tag never reaches our server.
The short version
The trafficked tag shows an empty slot, a broken creative or a mixed-content warning on the publisher page, and the cause is usually in the tag text itself: curly quotes from an email, an http:// URL, a half-replaced macro, an HTML-escaped paste.
Check your creative now: ZIP, folder or ad tag
LOCALYour browser reads the file. Nothing is uploaded.
Preflight check
Drop a creative ZIP or folder here
One creative at a time. The verdict appears right here.
- Running calls the ad server, the same request a real impression makes. It may count one.
- An empty slot can be targeting (domain, region, frequency cap), not a broken tag.
Check the tag text before it runs
- •Tag markup: straight quotes, and every element that opens also closes.
- •Secure URLs: every URL in the tag is HTTPS.
- •Macros: no broken macro, no leftover placeholder, no mix of two platforms' macro styles.
- •Ad size: exactly one size declared, and whether it is an IAB standard size.
- •Click tracking: an empty click macro slot is flagged; a filled one is reported.
- •Asynchronous loading: tags that write the ad with document.write are flagged.
- •Not a tag: a full HTML page or an HTML-escaped paste is caught with a sentence saying what to paste instead.
The tag checks read the pasted tag as text and answer instantly. A failure here is shown before the Run button, because running a broken tag shows nothing useful. The ad server is recognised from what the tag loads, so the result reads "CM360 tag · 300×250".
Preview the tag live, in a sandbox
Run tag loads the tag in a sandboxed iframe sized to the slot: it can run its scripts, but it cannot reach the page, open popups or redirect. Your browser calls the ad server just as a real impression would, and the slot shows the ad it serves.
While it runs, the page reports what a browser can see from outside the ad's frame: whether the slot filled and how fast, insecure requests, errors in the tag's own frame, and whether the ad stays inside its slot.
The desktop app goes further: it captures the creative the tag actually served and runs the full standard check and the Deep Audit on it - JavaScript errors, blank render, CPU and network against Chrome's Heavy Ad limits.
What Ad-Preflight checks
- ✓Tag markup, curly quotes and unclosed elements
- ✓HTTPS on every URL in the tag
- ✓Broken macros and leftover placeholders
- ✓Declared size against the IAB list
- ✓Click macro and click tracker slots
- ✓document.write and synchronous tags
- ✓Live preview: slot filled, insecure requests, frame errors
What it cannot guarantee
- !The ad server may count an impression when the tag runs
- !An empty slot can be targeting (domain, region, frequency cap), not a broken tag
- !The browser sees the served ad only from outside its frame; the desktop app checks the creative itself
- !VAST and video tags are not checked yet
Run it in the desktop app
Designers and AdOps can drop a campaign folder or paste an ad tag into the desktop app and follow the visual report.
- 1.Paste the tag into the check, exactly as the ad server exported it.
- 2.Fix any failing tag check before running it.
- 3.Press Run tag and watch the slot fill in the preview.
- 4.For runtime checks on the served creative, paste the same tag into the desktop app.