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

Annotations already declare readOnly, non-destructive, open-world behavior, so the safety profile is covered. The description adds genuinely useful behavioral context: pages hold up to 200, cursoring is implied, and it requires the user's Cotlet API key with app access. Return-item structure (user_id per item) is also disclosed.

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?

Front-loaded and short, but the opening two sentences overlap heavily ('People you can invite: your past guests and mutuals' vs 'Returns people you can invite again: guests who attended your events and mutuals'), repeating the same idea instead of each sentence earning its place.

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?

With no output schema, the description supplies the essential return context (people objects carrying user_id), pagination size, cursor paging, and authentication requirements. That is sufficient for correct invocation, though it leaves the relationship to partiful_list_guests unaddressed.

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 100%, so the schema already documents limit, query, cursor, and from_event_id. The description's parameter content ('pages hold up to 200', filtering to one past event) largely restates the schema, adding only mild rationale for from_event_id. Baseline 3 fits when the schema carries the parameter burden.

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 and resource (list past guests and mutuals) with scope detail, and explains the optional per-event narrowing. It is clear what the tool returns, but it never names the likely-confusable sibling partiful_list_guests, so an agent must infer the distinction.

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?

Provides clear context: use it to get people you can re-invite, and it tells the agent to consume the returned user_id with invite_guests. It also explains when to filter by a single past event. It lacks an explicit when-not-to-use or a direct alternative comparison against partiful_list_guests.

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