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

Annotations only supply destructiveHint=true; the description explains the source of that destructiveness (message is delivered to the guest through Airbnb/Booking.com/Vrbo/email and cannot be unsent) plus the private-note alternative. It adds real behavioral value, though it omits auth requirements, rate limits, and what a successful send returns.

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 sentences, no filler, with the primary action first, the mode-dependent behavior second, and the endpoint reference last. Every clause carries information the caller needs.

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 and only a destructiveHint annotation, the description carries the necessary burden and does so: it covers both modes, their audience, irreversibility, and the underlying API path. Nothing material is missing for correct invocation.

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 parameters are already documented, and the description largely restates the source enum semantics. It adds the channel-delivery implication of source=host, but no new syntax or constraints beyond the schema, so the baseline 3 applies.

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 (send) and resource (a message on a booking's conversation), and the description's two-mode framing clearly separates this from sibling readers like beds24_list_booking_messages and beds24_mark_messages_read. An agent can tell what this tool does without opening the 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?

It gives explicit conditional guidance on the two modes (default source=host delivers to the guest; source=internalNote is a private note) and the consequence that selecting host cannot be undone. It does not explicitly route the agent away from related siblings such as mark_messages_read, so it stops short of full when/when-not coverage.

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