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

Annotations declare readOnlyHint=true, so safety is already covered; the description adds genuinely new behavioral context: 'Cursor-paginated' and the underlying endpoint GET /api/v3.3/messages, which tells the agent this is a paged read against an upstream API. It does not discuss rate limits, ordering, or empty-result behavior, keeping it short of a 5.

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 tight sentences with zero filler: purpose first, scoping instruction second, pagination note third. The endpoint reference is appended compactly rather than expanded into prose.

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?

There is no output schema, and the description compensates by naming the returned fields ('sender type, status and content') and the pagination mechanism. For a 6-param, all-optional read tool with readOnlyHint set, an agent has everything needed to call it correctly.

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%, and each schema description is already specific ('Only messages about this lead.', 'Cursor from the previous page's _paging._nextCursor.'). The description restates the lead/thread/agency scope and pagination but adds no format or interaction detail beyond the schema, so the baseline 3 is right.

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 (read/list) and resource (guest messages) plus the channels covered (Airbnb, VRBO, Booking.com, email, SMS, WhatsApp, in-app) and the three scoping axes (lead, thread, agency). The lead/thread/agency framing implicitly separates it from the sibling hostfully_list_threads and hostfully_list_reviews, so an agent can route without opening schemas.

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?

'Give lead_uid, thread_uid, or agency_uid (or the default)' makes the scoping choice explicit and tells the agent a fallback exists when no identifier is supplied. It stops short of naming a sibling alternative or stating when not to use this tool (e.g., versus hostfully_list_threads for thread metadata), so it is clear context without exclusions.

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