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

Annotations already declare the safety profile (not read-only, not idempotent, not destructive, closed-world), so the description could have added the remaining behavioral context instead of restating the action. It says nothing about whether a sent message can be edited or retracted, what happens if the conversation is closed, or any rate limits. The one useful addition, safe retry via idempotency_key, lives in the schema rather than the description.

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?

A single short sentence with no filler, and the precondition is front-loaded in the same clause as the action. It is efficient but so terse that it borders on under-specification rather than tight writing.

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, so the description is the only place an agent could learn what a successful send returns (a message id, a delivery status) or how failures surface. For a state-changing messaging tool it covers the what but leaves the outcome and error behavior 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 all four parameters including the idempotency_key retry semantics are already fully documented in structured fields. The description adds no syntax, format, or constraint detail beyond that, so the baseline of 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+resource pair ("add a message to a conversation") and ties it to a prerequisite established by the sibling contact_owner. An agent can tell it appends to an existing thread rather than opening one, though it never explicitly contrasts with check_reply or the other siblings.

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 phrase "conversation you opened with contact_owner" implies the prerequisite (contact_owner must run first) and the context (follow-up, not initial contact). But there is no explicit when-to-use/when-not statement, no guidance on distinguishing a follow-up from a reply or from re-contacting via contact_owner.

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