Why is the byte size 0 for some requests?

Sizes come from the Resource Timing API. Browsers only expose transferSize for cross-origin resources when the server sends a Timing-Allow-Origin header, so third-party pixels often report 0 bytes. Durations and start times are still accurate.

Does clicking the creative open the landing page?

No. Every anchor click, form submit and window.open call is intercepted and recorded in the Clicks tab with the macro-expanded URL. You can open a captured URL manually from there.

Which macros are substituted?

%%CACHEBUSTER%%, [CACHEBUSTING], [RANDOM], [TIMESTAMP], %%CLICK_URL_ESC%%, %%CLICK_URL_UNESC%%, %%CLICK_URL_ESC_ESC%%, {{CLICK_URL}} and every OpenRTB ${AUCTION_*} macro. The cachebuster is regenerated on each Render and Reload; unknown macros are left untouched so you can spot them.

Can I see requests made inside a nested iframe?

Only the iframe load itself is visible. Requests fired from inside a friendly iframe or SafeFrame are isolated by the browser. Paste the JavaScript form of the creative to see its full request tree.

Ad Tag Tester

Paste an HTML or JavaScript ad tag, an iframe tag, or a bare creative URL, pick an IAB slot size and render it inside a sandboxed iframe. The tester expands ad-server macros (%%CACHEBUSTER%%, [TIMESTAMP], %%CLICK_URL_ESC%%, ${AUCTION_PRICE}…), then records every pixel, script and iframe the creative loads (URL, initiator, size, timing, grouped by domain with an http warning), captures click-through URLs without navigating, mirrors console output and errors, reports the load event and the rendered size, and keeps the last 10 tags in your browser. VAST markup is detected and handed to the VAST Inspector or IMA player instead.

Runs locally in your browser

Render an ad tag in a sandboxed frame and watch every request, click and console line it produces

Slot sizeClick URL macro

${AUCTION_PRICE}Cachebuster (auto)

Ad tag (HTML / JavaScript)

0 chars · 1 line

300 × 250

Nothing rendered yet.

No network requests captured yet. Render a tag to see every pixel, script and iframe it loads.

Requests

Bytes

—

Domains

Load

—

Errors

Clicks

Bid Response Inspector

Decode an OpenRTB BidResponse: bids, macros, no-bid reasons, creative preview and win/billing notice firing.

VAST Ad Tester (IMA Player)

Play any VAST or VMAP tag in a real Google IMA player and watch every SDK event, error and timing.

VAST Inspector

Fetch or paste VAST 2/3/4 tags — follow wrapper chains, validate, ping pixels, and play media files.

OpenRTB Inspector

Validate & annotate OpenRTB 2.6 BidRequest and BidResponse JSON.

URL Parser & Query Editor

Break any URL into parts, edit query params live, unwrap nested redirect URLs, decode ad macros, build UTMs and follow redirects.

How to use Ad Tag Tester

1Paste an HTML/JS ad tag, an <iframe> tag or a creative URL, or load one of the samples.
2Pick a slot size (IAB presets, responsive fill or custom w×h) and optionally set a click URL and ${AUCTION_PRICE}.
3Press Render (⌘/Ctrl+Enter). Use Reload to run the tag again with a fresh cachebuster.
4Read the Network, Console, Clicks, Timing and DOM tabs, then export the request list as CSV.

About Ad Tag Tester

Ad Tag Tester is part of FizzKit — a collection of focused developer and ad-tech tools. Because everything runs locally, it works offline once loaded and never exposes your data to a remote server.

Frequently asked questions

The creative runs in an iframe with sandbox="allow-scripts allow-popups" and an opaque origin: no cookies, no localStorage, no window.top access and no referrer. Tags that require cookie sync, read the top window or check the referrer behave as they do on a strict publisher page and may refuse to render. The Console tab usually shows the reason.

Related tools