Basis HTML5 banner specs

US-headquartered demand-side platform, formerly Centro, buying display, video, audio and native inventory. Hosts an HTML5 ZIP directly or takes an ad tag, caps the uploaded package at 1 MB, and reads the click destination from a `clickTag` or `clickTAG` query parameter on the ad URL rather than rewriting the file. HTML5 runs inside an iframe, so the creative cannot touch the parent page.

Sourced from Basis documentation · 23 September 2026Foldwrap exports to Basis

Also known as Basis Technologies, Centro, Basis DSP, Centro DSP, Basis Platform, Centro.

Check a ZIP against Basis Export a bundle for Basis

Basis banner requirements

Category	DSP
Regions	US, CA
Maximum ZIP size	1 MB zipped
Entry file	index.html
ZIP structure	Entry file must sit at the ZIP root
Click method	clickTag on the ad URL
Click variable	clickTag
Click URL query parameter	clickTag
Click URL at export	Left empty — the platform sets it when the ad is trafficked
Multiple click destinations	One click area per banner
Maximum animation length	15s
Maximum loops	3

Official requirements Also from Basis: HTML5 Ads (Help Center), Ad Specifications (Help Center), Creative Policy (Creative Policy - Centro), IAB HTML5 for Digital Advertising v2.0.

Basis clickTag code

This is the click declaration Foldwrap writes into an HTML5 export for Basis, with a placeholder destination. Copy it into your own creative if you are hand-building the banner.

Basis clickTag

var clickTag = (function () { var m = new RegExp('[?&]' + "clickTag" + '=([^&]*)', 'i').exec(window.location.search); return m ? decodeURIComponent(m[1]) : "https://www.example.com/landing"; })();

Basis sets the destination at trafficking time, so an empty value in the exported file is correct and expected.

Why Basis rejects a banner

These are the rules Foldwrap checks a package against before it is delivered to Basis. Each is derived from the requirements above, so a constraint Basis does not state is not checked and is not listed.

errorAnimation runs longer than allowedShorten the timeline or reduce the loop count.
errorClick is not wired for this platformDeclare clickTag in the creative and open it on click.
errorEntry HTML is not at the ZIP rootRe-zip the contents, not the containing folder.
errorExceeds size limitCompress images, subset fonts to the glyphs actually used, and drop unused assets.
errorNo entry HTMLAdd index.html at the ZIP root.
errorReferenced asset is not in the packageRe-export the creative so every referenced asset is bundled.
errorToo many animation loops
warningElement destinations flatten hereKeep a target that supports element destinations in the set, or set a default click URL that suits every element.

Foldwrap runs these checks on every package it exports for Basis, and names the creative and the constraint when one fails.

Sources

Every figure above, with the document it came from and the date we read it.

JavaScript code inside the HTML5 files must read the clicktag from a query string parameter named clickTag or clickTAG.
help.basis.com · retrieved 23 September 2026
All links must open in a new window
legal.basis.net · retrieved 23 September 2026
Maximum file size that can be uploaded | 1024 KB (1 MB)
help.basis.com · retrieved 23 September 2026
The ZIP file must be smaller than 1 MB.
help.basis.com · retrieved 23 September 2026
The primary HTML file must be in the root directory of the ZIP file.
help.basis.com · retrieved 23 September 2026
If there is only one HTML file (*.html or *.htm), it is the primary HTML file. If the ZIP contains multiple HTML files, the primary file must be named "index.html".
help.basis.com · retrieved 23 September 2026
No more than 15 seconds or 3 loops.
help.basis.com · retrieved 23 September 2026
No more than 15 seconds or 3 loops.
help.basis.com · retrieved 23 September 2026

Frequently asked

What is the maximum file size for a Basis HTML5 banner?

Basis accepts an HTML5 package up to 1 MB zipped. Note what the cap measures: a bundle can compress under the limit and still be refused if the figure is taken unzipped.

How do I set the clickTag for Basis?

Declare clickTag in the creative. Basis replaces the value when the ad is trafficked, so exporting with an empty destination is normal and correct.

Can a Basis banner have more than one clickable link?

No. Basis takes a single click destination for the whole banner, so every click goes to the same page regardless of which element was clicked.

Other platforms

Compare every platform side by side, or produce a Basis-ready bundle from an approved Figma design with Foldwrap.