Valid tool schemas across the web

Sites whose WebMCP tools declare a schema that validates. It has gone up since July 2026, by more than the margin allows us to call a wobble — though last month on its own did not move.

Excellent98.5%

Valid tool schemas in September 2026

What the Valid tool schemas in September 2026 is, and how it is measured

Measured on 7,237 pages, 4.4% of which carried the agentic category, with a confidence margin of ±0.62 pp.

= −0.1 pp

96.2%98.5%

Valid tool schemas, July 2026 to September 2026, one measurement a month. The last step was inside the margin, so it is a tie.

What this measures

Lighthouse audit: webmcp-schema-validity

Of the sites that register WebMCP tools, those whose tools declare a schema that validates. An agent can call a tool without a schema but does not know what with. Informative mode too, so it is invisible to the category score.

Who moved

How to read these figures

Every figure here comes from a sample, not from counting every site — so it carries a margin: how much it could move if we had happened to sample different pages. A figure measured on a thousand pages has a wide margin; one measured on a hundred thousand has a narrow one. It matters for one thing: two figures that differ by less than the wider of their margins are not one above the other, they are tied. That is why nothing here has a position number.

How many actually moved

0 of the 1 segments measured on both months moved by more than their margin. The other 1 did not move: their difference is smaller than this sample can resolve. All of them are in the table below.

Nobody moved

Every one of the 1 segments stayed inside its margin. The figure for the web overall can still move while none of its parts do — the corpus is measured on far more pages than any single segment, so it resolves smaller changes.

From Omitsis, who publish this census

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