To check an HTML5 ad before it goes live, open the creative in a validator that reads its dimensions, clickTag setup and tag markup, then fix anything that fails before you hand it to a publisher. HTML5 Ad Inspector does that work in your browser: drop in a ZIP, paste an iframe or script tag, or enter a creative URL, and it inspects what you gave it without uploading the file anywhere.
Most rejected ads fail for boring reasons — a missing clickTag, a size that does not match the placement, a backup image that never loads. Catching those five minutes before trafficking is the whole job.
What an HTML5 ad check actually looks for
A useful HTML5 ad validator answers four questions:
- Is the size right? The creative canvas has to match the placement you bought — 300x250, 728x90, 160x600, 320x50 and so on. A 1-pixel mismatch can cause a rejection or a stretched banner.
- Does the clickTag work? The exit URL has to be wired the way the network expects, and the click area has to cover the whole ad, not just the button.
- Do the files resolve? Every image, font and script the ad references should load from relative paths inside the ZIP, not from a local folder on your laptop.
- Is the tag markup sane? If you are checking an iframe or script tag, the inspector reads the markup itself rather than the creative behind it.
That is the difference between an HTML5 banner checker and a screenshot. You are not looking at how the ad looks; you are looking at whether it will run.
How to check an HTML5 ad with HTML5 Ad Inspector
- Open HTML5 Ad Inspector. You will see a drop zone labelled 'Drag & drop or browse', under the line 'Processed locally — your files never leave your device'.
- Add your file. Drag your exported ZIP onto the drop zone, or browse to it. If you are checking a live tag instead, paste the iframe or script tag, or enter the creative URL.
- Run the inspection. The page reads the creative from your own machine and reports what it finds.
- Read the size result first. Confirm the canvas dimensions match the placement you are trafficking to. If you exported a 300x250 into a 336x280 slot, you will see it here rather than in a publisher rejection email.
- Check the clickTag. Confirm the exit URL is present and that the click layer covers the full creative. A clickTag that only fires on the button is the single most common HTML5 rejection.
- Check that assets resolve. Missing images and fonts usually mean an absolute path pointing at your desktop instead of a relative path inside the ZIP.
- Fix, re-export, and re-check. Repeat until the report is clean, then hand the ZIP to whoever traffics it.
If you are inspecting several creatives at once, HTML5 Ad Inspector takes multiple files. Free plans process up to 3 files per batch without an account or 5 with one, and a whole batch counts as a single run. That matters when you have a full set of sizes to clear before a campaign start.
Checking an ad tag rather than a ZIP
Not every check starts with a ZIP. Three inputs are common:
- A ZIP — the exported creative package, which is what most designers hand over.
- An iframe or script tag — what you paste into a tag manager or a publisher's ad slot.
- A creative URL — a hosted creative you want to sanity-check before it goes into rotation.
For an iframe ad tag check, the useful question is whether the markup is well formed and points where you think it points. A tag that loads a 404, or that nests an iframe inside an iframe for no reason, will fail at the publisher even though it looked fine in your test page.
For a Google Ads HTML5 validator pass, the same rules apply: Google's requirements around clickTag naming and file structure are strict, and a quick local check saves a round trip through review.
Why checking in the browser beats upload-based ad checkers
Most online ad validators ask you to upload the creative to their server. That has three practical costs.
Privacy and confidentiality. An unreleased campaign is commercially sensitive. Uploading it to a third-party validator means it sits on someone else's infrastructure, sometimes for hours, sometimes indefinitely. With local processing, the file is opened from your own machine and the work happens in the page. Nothing leaves your device.
Speed. A 2 MB ZIP does not need a round trip to a server and back. Local inspection is effectively instant, which matters when you are clearing a dozen sizes at 6pm before a launch.
No file-size caps. Upload-based tools often impose a limit, and rich HTML5 creatives with embedded video or high-resolution assets get large fast. There is no file-size cap here, so a heavy creative is not a problem.
One more thing worth knowing: a run is one export, however many files it contains. Free plans process up to 3 files per batch without an account or 5 with one, and a free account raises the daily allowance from 5 runs to 15. Pricing covers unlimited daily use if you clear creatives every day.
Common mistakes that get HTML5 ads rejected
- A clickTag that only covers the button. The expected behaviour is a transparent click layer over the whole creative. Test by clicking the corner of the ad, not the middle.
- Absolute paths. Anything referencing
C:/Users/...or a local server will break the moment the ZIP is opened elsewhere. - The wrong exit URL in the wrong size. When you export a set, it is easy to leave last campaign's URL in one variant. Check every size, not just the hero.
- A missing backup image. Some networks require a static fallback. If the ZIP does not include one, that is a rejection waiting to happen.
- Uncompressed assets. A 6 MB banner for a 300x250 slot will pass a size check and still get flagged for weight. Compress before you export.
- Checking only the ZIP. If you also paste the tag into a tag manager, check the tag too — the ZIP can be perfect while the tag points at the wrong file.
Where this fits in a normal ad production flow
A practical order of operations for a campaign:
- Design at the largest size, then adapt.
- Export each size as its own ZIP.
- Check every ZIP with HTML5 Ad Inspector in one batch.
- Fix and re-check anything that fails.
- Hand the clean set to trafficking.
If your creative started life as a screenshot or a static design, Mockup Generator is useful for presenting it in a phone, browser or laptop frame for client review — a different job from validation, but it often happens in the same week. When the same design needs to go out to every social placement as well as the display buy, Social Pack Exporter exports one design to every social size in a single pack, which keeps the size list in one place. And if the campaign includes audio, Podcast Artwork Pack turns one square of cover art into every size Apple, Spotify and your host ask for.
None of that replaces the validation step. Presentation tools make an ad look right; an HTML5 banner checker makes it run. The two are easy to confuse, and confusing them is how a campaign goes live with a dead clickTag.
The habit worth building is simple: never hand over an HTML5 creative you have not opened yourself. It takes under a minute per size, it runs on your own machine, and it catches the class of error that publishers reject automatically without a human ever looking at your work. A creative that fails a clickTag check never gets seen by anyone — which is the most expensive kind of failure in display advertising.