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

The destructiveHint annotation is already present, and the description reinforces it with 'MUTATES OwnerRez data' rather than contradicting it. It adds genuinely non-structured context: the write endpoint, that the thread/booking linkage is account-specific, and that the created message is returned. It does not cover auth requirements or reversal/undo behavior, which keeps 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 the mutation warning front-loaded, followed by endpoint, linkage caveat, and return value. Slight redundancy in restating the mutation that destructiveHint already signals, but no filler.

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 write with no output schema, the description covers the mutation, the endpoint, the linkage subtlety, and the return value. It omits any mention of permissions/scope needed to post to a thread, which is the main remaining gap.

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 baseline is 3, but the description goes further by explaining the otherwise opaque `fields` bag — it tells the agent to route thread_id/booking_id-style linkage through it. That is real added meaning beyond the generic schema text for `fields`.

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 ('posts a message into a guest-communication thread') and even names the backing API operation POST /v2/messages. An agent can distinguish this from create_booking, create_guest, and list_messages without opening 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 explains HOW to supply account-specific linkage (via `fields` with thread_id/booking_id), which is useful operational guidance, but never states WHEN to use this tool versus alternatives like ownerrez_request or list_messages. Usage is implied by the thread/booking framing rather than stated.

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