What Is TagManifest? A Free Google Tag Manager Scanning Tool

How TagManifest started

In 2023, I was handling a wave of Universal Analytics to GA4 migrations. Different companies, different industries, same story: nobody fully owned the GTM container.

The last agency had set it up. Or a developer who left two years ago. Or marketing had been making changes while IT occasionally stepped in to fix things. The container worked, mostly, but nobody could explain exactly what was in it or why.

There was no documentation. No naming conventions anyone had stuck to. Tags from three different eras, each with their own logic. The first step of every migration was the same: open the container, stare at 100+ tags, and start reverse-engineering what everything did.

That manual audit pass is what TagManifest replaces.

GTM is a hot potato

Google Tag Manager is foundational. Analytics, consent management, conversion tracking, marketing pixels: it all runs through GTM. But ownership is murky. Marketing needs it configured correctly. Development has to implement the data layer. Legal cares about consent compliance. And nobody considers it their primary responsibility.

That ambiguity makes containers messy. Not broken, usually. Just messy in ways that make them hard to understand and harder to hand off. When someone new inherits a container (and someone always does), the first question is always the same: what am I looking at?

What TagManifest does

TagManifest is the first audit pass. Instead of opening every tag, trigger, and variable individually, you upload your container's JSON export and get the lay of the land in seconds.

The scan answers three questions:

1. What is this container? How many tags, which platforms, who's been working in it, how long has it been accumulating.
2. Is it doing its job? Are analytics collecting data? Is consent configured? Are conversions attributed? Is anything leaking PII?
3. What needs fixing, and in what order? Not a list of 50 problems sorted by severity. A work plan organized by effort: quick wins, focused fixes, structural work, and strategic improvements.

Consent is the reason this matters now

Consent Mode v2 and the Digital Markets Act have put the onus on marketing teams to get consent right. These are high-stakes configurations with legal consequences, and they sit inside the same GTM container that nobody fully owns.

TagManifest checks whether your CMP is wired up correctly, whether tags are firing with the right consent types, and whether ad platforms have the consent signals they need. It won't make you compliant on its own, but it tells you where the gaps are so you know where to focus.

Why it's free

I use TagManifest regularly in my own work. It saves me the manual audit pass every time I open a new container. I don't see why you shouldn't have the same tool.

The value is knowing where to start. That's a limited objective, and it's the right one for a free tool. TagManifest doesn't monitor your container over time or manage your tag deployments. It gives you an honest picture of what's in there right now.

Built to be secure

Your container data never leaves your browser. TagManifest runs entirely as client-side JavaScript. There's no server receiving your data, no database storing your scans, no account to create.

The tradeoff is that scans are stored locally in your browser. If you clear your data or switch machines, you'll need to run the audit again. That's an acceptable tradeoff for keeping your container configuration private.

Reports you and your AI tools can use

TagManifest gives you the audit in formats that are useful beyond the dashboard:

• Markdown report for documentation and sharing. A narrative that tells the story of the container in a format anyone can read.
• CSV export for remediation tracking. One row per finding per affected item, ready for a spreadsheet or project tool.
• MCP server for AI workflows. Feed your container data and diagnostic results into Claude, ChatGPT, or any LLM so they can answer questions, explain issues, and help you fix things.

The goal is to make the next step, actually fixing and organizing your container, as easy as possible.

How to use it

1. Export your container. In Google Tag Manager, go to Admin, then Export Container. Download the JSON file.
2. Upload and scan. Drop the file into TagManifest. The audit runs in seconds.
3. Read the dashboard. Start with the summary: functional health score, top priorities, and category status. Drill into consent, measurement, events, or infrastructure for detail.
4. Export your results. Download the markdown report or CSV. Share with your team, or feed the data to an AI agent for help with remediation.
5. Fix what matters first. The work plan tells you what's quick, what takes a day, and what's a project. Start with the quick wins.

What's next

TagManifest is a working tool, not a finished product. We're improving it as we go:

• Better dashboard visualizations. Clearer ways to see consent coverage, event flows, and container complexity at a glance.
• Community feedback. We want to hear what's useful, what's missing, and what doesn't make sense. The rules engine is open source for a reason.
• Container documentation. Generating documentation from your container data, so the next person who inherits it has a head start.

I've needed this tool many times in my career. I hope it solves a problem for you too.

TagManifest: A Free Scanner for Messy Google Tag Manager Setups

TagManifest was born out of a simple, repetitive problem: every new Google Tag Manager (GTM) engagement started with opening a container, staring at 100+ tags, and manually reverse‑engineering what everything did. Different companies, different industries, same pattern—no one fully owned the GTM setup, documentation was missing, naming conventions were inconsistent, and tags from multiple eras coexisted with their own logic. TagManifest replaces that manual first pass with an automated scan.

The Problem: Foundational, Neglected GTM Setups

GTM runs on roughly 46.6% of all websites and sits at the center of analytics, consent management, conversion tracking, and marketing pixels. Yet ownership is fragmented: marketing needs it configured, development owns the data layer, and legal cares about consent. Because nobody treats GTM as a primary responsibility, setups become messy—not necessarily broken, but hard to understand and harder to hand off. When someone new inherits a container, the first question is always: what am I looking at?

What TagManifest Does

TagManifest is a free GTM scanning tool. You enter a website URL, a GTM container ID, or both, and it quickly answers three core questions:

1. What is this setup?

• How many tags exist
• Which platforms are in use

Two Ways to Scan

1. Enter a URL

TagManifest fetches the page, discovers the GTM container automatically, and runs a full scan of both the container and the page. You get:

• Detection of major Consent Management Platforms (12 CMP vendors including OneTrust, Cookiebot, CookieYes)
• Detection of tracking scripts loading outside GTM (e.g. gtag.js, HubSpot, Meta Pixel, LinkedIn, and others)
• Inspection of consent defaults in the page source

2. Upload a JSON export

Export your container JSON from the GTM admin panel and upload it for the deepest analysis. This unlocks all 93 checks, including:

• Tag names and folder structure
• Checks that require the full container definition

JSON uploads are processed entirely in your browser.

Why Consent Is the Critical Use Case

Consent management spans multiple layers:

• A CMP may load on the page via inline script (as recommended by tools like OneTrust and Cookiebot)
• Consent settings on tags inside GTM are configured separately
• Native Google tag templates enforce consent automatically
• Custom HTML tags default to no consent and stay that way unless explicitly configured

TagManifest checks all of these layers:

• Whether a CMP exists on the page
• Whether consent defaults are set before GTM loads
• Which tags have consent configured inside the container
• Where the gaps are between page‑level and container‑level consent

When a page‑level CMP is detected, TagManifest adjusts its findings so container‑only consent warnings don’t mislead you when consent is actually managed outside GTM.

In research across ~2,000 B2B SaaS containers, TagManifest found:

• 56% of sites had no consent management detected anywhere
• Among sites with consent, 80% of Custom HTML tags had no consent configured inside GTM

The structural issue: native templates enforce consent; Custom HTML does not.

Why TagManifest Is Free

TagManifest is a practical tool used in ongoing consulting work to avoid repeating the same manual discovery process for every new GTM container. The core value is knowing where to start—getting an honest snapshot of the current setup and a prioritized work plan.

Research-Backed Scanning Engine

TagManifest’s scanning logic is grounded in real‑world data. The engine has been tested against more than 2,200 GTM setups across B2B SaaS and the Fortune 500. The research findings, including methodology and limitations, are published publicly and directly inform:

• Which checks matter most
• How to interpret consent across multiple layers
• What typical GTM setups look like at different scales

This research‑backed approach keeps the tool focused on issues that actually show up in production containers.

Reports for Teams and AI Tools

TagManifest outputs results in formats designed for both humans and AI assistants:

• Markdown report – A narrative overview of the setup, suitable for documentation and sharing with non‑technical stakeholders.
• CSV export – One row per finding per affected item, ready for spreadsheets or project management tools to track remediation.
• AI‑ready folder export – Structured JSON files plus a CLAUDE.md that explains how an AI agent should read the data: start with the profile, review Custom HTML code, then verify findings. You can feed this into tools like Claude, ChatGPT, or Cursor to help interpret and fix issues.

How to Use TagManifest

1. Enter your URL or GTM ID on the scan page. TagManifest will auto-discover the container when given a URL, or you can paste your GTM container ID directly.
2. Review the scan summary: check the health score, consent status, top priorities, and category status, then drill into consent, measurement, events, or Custom HTML for detailed findings.
3. If you started with only a container ID, add your website URL to enable CMP detection, tracking-outside-GTM detection, and verification of consent defaults.
4. Export your results as a markdown report, CSV, or AI-ready folder to share with your team or pass to an AI agent for remediation.
5. Use the work plan to prioritize fixes: tackle quick wins first, then the tasks that take a morning, and finally the larger project-level items.

Start Scanning Your GTM Setup

Go to TagManifest, enter your URL or GTM container ID, and get a clear, prioritized view of what’s in your Google Tag Manager setup. It’s free and doesn’t require an account.