# Banner Check by Viewst

> A free, in-browser HTML5 banner preflight tool. It validates display ad creatives against the real upload requirements of 28 ad networks before you submit them to a DSP. No backend, no account, no file upload to a server — everything runs client-side in the browser.

## What it does

Banner Check checks an HTML5 banner — uploaded as a ZIP archive, a single HTML file, or pasted markup — against a chosen ad network's ruleset. It reports pass, warning, or error for each check, with a plain-English reason and a suggested fix, plus a live sandboxed preview of the rendered banner.

### Checks performed

- **File size**: Packaged (zipped) weight vs. the network's limit. Amazon DSP also measures the uncompressed initial load; that case is flagged separately.
- **Structure**: Presence of index.html, required special files (manifest.json for BidTheatre, index.js for Amazon DSP 2.0), and absence of nested zip-of-zips.
- **Dimensions**: Banner size read from `<meta name="ad.size">`, the filename, and CSS. Errors when the meta and filename disagree.
- **Required tags**: `<meta name="ad.size">`, the network's required vendor `<script>`, and the `#bannerClick` wrapper element.
- **Click integration**: Network-aware. Validates standard `clickTag`, query-param `getParameterByName`, vendor SDK calls (Amazon `SDK.clickThrough`, Xandr `APPNEXUS.getClickTag`), or ad-server macros.
- **External URLs**: Flags external references. For Amazon DSP any non-allowlisted host is an error (the most common DSP rejection reason); for other networks it is an informational notice (you decide whether to bundle them — it does not fail the check).

## Use it programmatically (AI agents & CLI)

The browser tool runs client-side and needs a human at the keyboard. For automation — and for AI coding agents that need to check or fix a banner without a browser — the **same validation engine** ships as an installable agent skill and command-line tool. It runs on Python with no dependencies (a Node fallback is bundled), so an agent can use it on almost any machine.

- Skill repo: https://github.com/viewst/validate-banner-skill
- Install into your agent (Claude Code, Cursor, Codex, Copilot, …): `npx skills add viewst/validate-banner-skill` — or `git clone` and copy `skills/validate-banner/` into the agent's skills dir.
- Run directly as a CLI: `python3 validate.py <banner.zip | banner.html> [options]`.
- **Check** a banner: `validate.py banner.zip` (auto-detect network) · `--network <id>` (one network) · `--all` (compatibility matrix) · `--json` (machine-readable). Exit codes: 0 pass/warnings, 1 errors, 2 usage/IO.
- **Optimize / fix** a banner: `validate.py banner.zip --network <id> --fix` — strips non-whitelisted external URLs (the #1 Amazon DSP rejection) and compresses oversized images to fit the size limit, writing a fixed copy (it never edits the input).
- Agent-oriented guide for the skill: https://raw.githubusercontent.com/viewst/validate-banner-skill/main/llms.txt

## Live browser tools (WebMCP)

When Banner Check is open in a browser with native WebMCP support, the top-level
page registers four tools through `document.modelContext`. This is a
progressive enhancement: the normal UI remains fully functional without WebMCP,
and every validation still runs locally in the tab.

- `list_supported_networks({})` — list supported network ids, labels, and package limits.
- `get_network_requirements({ networkId })` — return one network's size, click, script, special-file, and external-URL requirements.
- `validate_html_banner({ networkId, html })` — validate supplied HTML markup for one network without loading it into the visible preview.
- `get_current_validation({ networkId? })` — validate the ZIP, HTML file, or pasted markup already loaded in the visible validator.

Tool results are compact, versioned JSON-safe objects. They never contain the full
HTML, Blob/base64 asset contents, or JavaScript regular expressions. Banner-derived
results are marked as untrusted content for the invoking agent. Catalog,
requirements, and supplied-markup validation are read-only. Current-page validation
may update the selected network/report and is annotated as state-changing. Detailed
contract and local testing guide:
https://bannercheck.org/webmcp.md

## Supported ad networks and size limits

- 150 KB: Google Ads, Google Campaign Manager, DV360, Smart AdServer, Verizon, AdRoll, Xandr (AppNexus), BidTheatre, Choozle, Delta Projects, Sizmek, Ströer, Yahoo Ad Tech, Xandr Invest
- 200 KB: Amazon DSP, Amazon DSP 2.0, The Trade Desk
- 450 KB: Quantcast
- 2 MB: Beeswax

## Amazon DSP requirements (strictest network)

Amazon DSP rejects any HTML5 banner that references a non-Amazon external host. Every asset (fonts, images, scripts) must be bundled inline. The only external URLs permitted are: adkit-advertising.amazon (Amazon SDK loader), amazon-adsystem.com, amazon.com, and greensock.com (GSAP license comment). Amazon DSP 2.0 additionally requires the SDK loader, an index.js file alongside index.html, and click wiring via `SDK.clickThrough`.

## Google Ads requirements

Google Ads requires a standard clickTag: `var clickTag = "https://example.com";` declared in the banner, opened via `window.open(window.clickTag, "_blank")` on click. The file-size limit is 150 KB compressed. GSAP should be bundled internally rather than loaded from a CDN.

## Xandr (AppNexus) requirements

Xandr requires the AppNexus HTML5 library and click wiring via `APPNEXUS.getClickTag()`. The file-size limit is 150 KB.

## BidTheatre requirements

BidTheatre requires the asxhtml5 SDK, click resolution via `asxhtml5.getParam("clickTag", fallback)`, and a `manifest.json` file describing width, height, source, and name.

## Sizmek requirements

Sizmek requires the EBLoader script and click wiring via `getParameterByName("clickTag")` rather than a hardcoded `clickTag` variable.

## The Trade Desk requirements

The Trade Desk HTML5 banners have a 200 KB size limit and read the click URL from the request URL via `getParameterByName("clickTAG")` — note the capital TAG (case-sensitive). Page: https://bannercheck.org/validate/trade_desk

## SmartAdServer requirements

SmartAdServer requires the vendor script `ns.sascdn.com/diff/templates/js/banner/sas-clicktag-3.1.js` and a standard clickTag. Size limit 150 KB. Page: https://bannercheck.org/validate/smartadserver

## Delta Projects requirements

Delta Projects requires the vendor script `sting.de17a.com/html5.js` and a standard clickTag. Size limit 150 KB. Page: https://bannercheck.org/validate/delta_projects

## Quantcast / Beeswax requirements

Quantcast allows a larger 450 KB package; Beeswax allows up to 2 MB — the highest of any supported network. Both use a standard clickTag. Pages: https://bannercheck.org/validate/quantcast , https://bannercheck.org/validate/beeswax

## Google Campaign Manager / DV360 requirements

Both are 150 KB with a standard clickTag and no required vendor script (DV360 is Google's programmatic demand-side platform). Pages: https://bannercheck.org/validate/google_campaign_manager , https://bannercheck.org/validate/google_video_360

## Common HTML5 banner rejection reasons

- Packaged ZIP over the network's size limit (Amazon and others measure the compressed weight).
- Missing or malformed clickTag — or the wrong click variant for the network (standard `clickTag` vs `getParameterByName("clickTAG")` vs a vendor SDK like `SDK.clickThrough` / `APPNEXUS.getClickTag()`).
- Missing `<meta name="ad.size">`, or banner dimensions that don't match the declared size.
- External asset references (fonts/images/scripts loaded from a CDN). Fatal for Amazon DSP, which only allows amazon-adsystem.com, amazon.com, adkit-advertising.amazon and greensock.com.
- A missing required vendor script or special file (e.g. `manifest.json` for BidTheatre, `index.js` for Amazon DSP 2.0).

## Per-network validator pages

Each ad network has its own dedicated validator page with that network's specific
requirements, an upload form pre-scoped to it, and SEO context. URL pattern:
`https://bannercheck.org/validate/<network-id>`. Examples:

- https://bannercheck.org/validate/google_ads
- https://bannercheck.org/validate/amazon_2dsp (Amazon DSP 2.0)
- https://bannercheck.org/validate/xandr
- https://bannercheck.org/validate/bidtheatre
- https://bannercheck.org/validate/trade_desk

Other ids: google_campaign_manager, google_video_360, sizmek, smartadserver,
delta_projects, choozle, quantcast, beeswax, adroll, verizon, stroer,
yahoo_ad_tech, xandr_invest, default. The full list is in sitemap.xml.

## About

- Provider: Viewst (https://viewst.com) — an HTML5 display ad production platform
- Tool URL: https://bannercheck.org
- License: Free to use; no account required
- Privacy: Files never leave the user's browser. No upload, no telemetry, no server processing.
- Ruleset source: Rules mirror Viewst's live ad-network export pipeline, updated as networks change their requirements.