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

Annotations only declare write, non-destructive, open-world. The description goes well beyond: it discloses PATCH semantics ('changes the fields you pass and leaves the rest'), that setting rsvp_answers impersonates the guest while null removes an answer, that it is silent to the guest and reversible by a single call (consistent with destructiveHint=false), and that a Cotlet API key scoped to the app is required. That is exactly the extra context annotations cannot carry.

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?

Purpose is front-loaded and each sentence carries distinct information (scope, patch behavior, RSVP impersonation/removal, reversibility, auth). Slightly long, with the trailing API-key note being near-boilerplate, but nothing is redundant.

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 3-parameter mutation tool with a fully documented schema and annotations that only carry safety hints, the description supplies everything needed to call it correctly: field semantics, non-destructive patch behavior, reversibility without confirmation, and auth requirements. The only omission is the response shape, which is minor here.

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 100%, so the baseline is 3, and the description earns an extra point by adding meaning the schema does not state: that omitted fields are preserved and that null on rsvp_answers is the removal path. It does not clarify the string encoding of 'fields', which is the one 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?

States a specific verb (change/set/remove) and resource (guest) and enumerates exactly which aspects are mutable: contact details, party/plus-ones, and RSVP answers. This cleanly separates it from joy_add_guest (creation) and joy_get_guest (read) without needing to open any schema.

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?

The description gives clear operating context — it sends nothing to the guest and is reverted by one more call, 'so it runs without asking' — which tells the agent it may invoke it freely. It does not explicitly name sibling alternatives (e.g. joy_add_guest for new guests or joy_assign_guest_tags), so it stops short of full when/when-not routing.

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