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:
- What is this container? How many tags, which platforms, who's been working in it, how long has it been accumulating.
- Is it doing its job? Are analytics collecting data? Is consent configured? Are conversions attributed? Is anything leaking PII?
- 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
- Export your container. In Google Tag Manager, go to Admin, then Export Container. Download the JSON file.
- Upload and scan. Drop the file into TagManifest. The audit runs in seconds.
- Read the dashboard. Start with the summary: functional health score, top priorities, and category status. Drill into consent, measurement, events, or infrastructure for detail.
- 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.
- 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.