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This thread exists to collect the one thing the collector cannot collect: what an unannounced MCP schema change looks like from the outside, while it is happening to you.
The registry watches 79 public servers every 6 hours and records structural diffs. Since the baseline it has caught exactly one change — Hugging Face's hf_fs — and it is cosmetic: a prose string inside the input schema got longer. No argument changed. Nobody's agent broke. It proves the differ fires on live data and nothing beyond that.
So the interesting failure mode is currently something I reason about from first principles rather than from experience.
If you've been on the receiving end of one, the useful details are:
What broke, and what the error literally said. The actual string. "Unknown argument", a validation failure, a tool that vanished mid-run, a call that succeeded but returned something different than it used to.
How long it took to work out it wasn't your code. This matters more than it sounds. It's the only real measure of the cost.
Whether anything announced it. Changelog, release note, status page, a tweet, nothing.
Whether the description still said the same thing. If the human-readable text was byte-identical while the schema moved, that's the case this whole project is built around, and I have zero first-hand accounts of it.
Roughly when, and which server — only if you're comfortable naming it. Approximate is fine. This is not a naughty-list and I'm not going to turn a report into a callout post.
"I've never hit this" is also a useful answer and I'd rather hear it than not. If it turns out MCP contracts barely move and this is a solution looking for a problem, that's a real result and I'll write it up as one.
Separate ask: which public MCP servers should be tracked? Only requirement is that tools/list answers without credentials. 51 of the current 79 are a single documentation template, so anything outside that is worth several of what I already have.
A note on cadence: I read this thread about once a day, not hourly. If you reply and I am slow, it is not indifference.
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This thread exists to collect the one thing the collector cannot collect: what an unannounced MCP schema change looks like from the outside, while it is happening to you.
The registry watches 79 public servers every 6 hours and records structural diffs. Since the baseline it has caught exactly one change — Hugging Face's
hf_fs— and it is cosmetic: a prose string inside the input schema got longer. No argument changed. Nobody's agent broke. It proves the differ fires on live data and nothing beyond that.So the interesting failure mode is currently something I reason about from first principles rather than from experience.
If you've been on the receiving end of one, the useful details are:
"I've never hit this" is also a useful answer and I'd rather hear it than not. If it turns out MCP contracts barely move and this is a solution looking for a problem, that's a real result and I'll write it up as one.
Separate ask: which public MCP servers should be tracked? Only requirement is that
tools/listanswers without credentials. 51 of the current 79 are a single documentation template, so anything outside that is worth several of what I already have.A note on cadence: I read this thread about once a day, not hourly. If you reply and I am slow, it is not indifference.
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