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

Annotations already declare a safe, idempotent read, so the bar is lower; the description still adds real context — the management-permission requirement, nextCursor-based pagination, and the fact that phone numbers are never returned. The contactAccess state machine materially changes what the caller can do with each result.

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?

Dense but economical — bracketed permission note, semicolon-separated rules, and the contactAccess mapping all earn their place with no filler. Front-loading the permission prerequisite is defensible, though the lack of a leading purpose sentence makes the structure feel telegraphic.

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 read-only list tool with no output schema, the description covers the prerequisite, scoping rules, pagination, and the full contactAccess vocabulary plus the phone-number exclusion. Remaining gaps are the exact meaning of q and activityRef against a 0%-covered schema.

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 description coverage is 0%, so the description must carry the load. It explains scope semantics (public search threshold, private-activity restriction) and pagination via nextCursor, but leaves q and the required activityRef unexplained, so an agent must infer the query and activity-reference parameters.

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 jumps straight into constraints and the contactAccess taxonomy without a sentence stating that the tool lists/searches guest-invitation candidates for a given activity. The purpose is inferable from these fragments plus the name/title, but an agent gets no explicit verb+resource statement to anchor on.

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?

Strong operational guidance: it states the admin-permission prerequisite, the three scope modes, the constraint that public scope needs an active search of ≥2 characters and is forbidden for private activities, and how each contactAccess value governs whether/how a candidate can be invited. It stops short of naming sibling alternatives (e.g. update_guest_candidates, add_guest_candidates) to route between.

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