What structured data does this page actually declare?
One number: how many distinct types. Then the two facts that number hides — how many JSON-LD blocks are on the page, and how many of them a parser would refuse to read.
Counted, not scored. There is no “structured data health: 82%”, because there is no scale that number could be measured against.
The block nobody counts
A JSON-LD block that does not parse is invisible. It sits in the markup looking like structured data, it passes a glance, and it contributes nothing — because the first thing any consumer does is call a JSON parser and give up. One trailing comma is enough.
MurmSchema counts those separately from the ones that work, so the difference is a number rather than a hunch.
It walks the graph
A Product with an Offer, an AggregateRating, a
Brand and two Reviews inside it declares six types. A tool that reads
only the top level of each block reports one. On the product page used for the listing images,
three blocks declare thirteen types.
What it refuses to tell you
Every MurmTools extension refuses at least one number that other tools invent. This one refuses to tell you whether a rich result will appear.
Whether search shows one is decided by the engine, not the page: by the query, the competition, the crawl, and rules that are not published and change without notice. A tool reading your markup cannot know it, so MurmSchema prints an em-dash and the reason instead of a green tick that means nothing.
Free, with no paid tier. Two permissions — activeTab and
scripting — and no host permissions at all.
Questions
Why does it report more types than I have blocks?
Because it walks the graph rather than reading the top level of each block.
What counts as an unparseable block?
One whose JSON does not parse. A trailing comma is the usual cause, and it discards the whole block for every consumer that reads it.
Will it tell me if I will get a rich result?
No. That is the engine's decision, not the page's, and the panel says so with the reason.
Is it free?
Yes, with no paid tier, no account and no server.