Validate HTML5 banners for Default / Custom
Free in-browser validator for Default / Custom HTML5 banners. Check the 150 KB size limit, clickTag, dimensions, required scripts and external URLs against Default / Custom's real upload requirements before you submit — no upload, no account.
Upload your Default / Custom banner
ZIP, a single HTML file, or pasted code.
Add a banner to validate it for Default / Custom
Everything runs in your browser — files never leave your machine.
Default / Custom HTML5 banner requirements
Supported by Viewst- Package size limit
- 150 KB
- Click integration
- standard clickTag (var clickTag + window.open)
- Required vendor scripts
- none
- External URLs
- Permitted — external references are allowed (flagged for your awareness).
Requirements last verified · sourced from Viewst's live ad-network export pipeline.
Default / Custom HTML5 banners — frequently asked
What is the file size limit for Default / Custom HTML5 banners?
Default / Custom HTML5 banners must be 150 KB or smaller. The limit applies to the packaged ZIP archive submitted to the ad server — every image, font and script bundled inside counts toward it. Banner Check measures the compressed weight and flags an error if it exceeds 150 KB.
How do I implement the click handler for Default / Custom HTML5 banners?
Default / Custom uses a standard clickTag. Declare var clickTag = ""; in index.html and open it on click with window.open(window.clickTag). The ad server injects the real destination URL at serve time, so leave the value empty.
Why does Default / Custom reject HTML5 banners?
Default / Custom rejects HTML5 banners for a package over 150 KB; a missing or malformed clickTag; a missing <meta name="ad.size"> tag; banner dimensions that don't match the declared size; or external assets that fail to load when the ad serves. Banner Check checks all of these in your browser before you upload.
Does this validator upload my banner files?
No. The validator runs entirely in your browser — your banner files never leave your machine. There is no upload, no account and no backend.
Preflight Default / Custom creatives before you upload
Ad networks reject HTML5 creatives for small, avoidable reasons — an oversized package, a missing clickTag, the wrong banner dimensions, or an external font URL. This free validator checks your banner against Default / Custom's real requirements in the browser, so you catch problems before the ad server does. It is built by Viewst, an AI ad-production platform that exports Default / Custom-ready HTML5 banners at scale.
Need to check a different network? Use the full Banner Check to pick from every supported ad network, or jump to one below.