Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare this is a non-destructive, idempotent write (readOnlyHint=false, idempotentHint=true), and the description adds a meaningful consent constraint and notes the user-facing affordance ("a card they tap in Hem"). It does not say whether a new answer replaces a previous one, nor what a successful call returns, so the extra context is useful but partial.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, front-loaded with the action and the answer values before the consent restriction. The closing remark about it being a card tapped in Hem is a bit cryptic and the least load-bearing sentence.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a three-parameter mutation with no output schema, the description covers the action and the consent rule but leaves the effect of re-answering, the meaning of planId, and the response shape unaddressed. Adequate, not complete.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is only 33%: rsvp's enum and optionIds are already documented in the schema (optionIds more thoroughly than the description), while planId is undocumented in both places. The phrase "which options work" adds little beyond the existing schema description, so the description only partially compensates for the coverage gap.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific verb and resource ("Answer a plan") and enumerates the exact answer set (yes, maybe, no) plus the option-selection behavior, so an agent knows this records an RSVP rather than reading a plan. It does not explicitly distinguish itself from siblings like rsvp_event or read_plan, which keeps it below 5.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives an explicit precondition and exclusion: only answer on behalf of the person with their own answer, and ask first otherwise. That is clear when-to-use guidance, though no alternative tool (e.g., rsvp_event for events, read_plan for viewing) is named.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.