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

Annotations already declare this is a non-read-only, non-destructive, closed-world write. The description adds the key behavioral fact those annotations cannot express: the note is internal-only and “never sent to the contact,” which is exactly the risk an agent needs to understand before writing. It stops short of saying whether the note is editable/deletable afterward or where it surfaces in the timeline, so it is strong but not exhaustive.

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 short sentences, front-loaded with the core action and visibility scope, then the sibling routing. Every sentence carries information; nothing is redundant with the title or annotations.

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 two-parameter write tool with fully documented schema, annotations covering the safety profile, and an output schema handling return values, the description covers everything needed to call it correctly: what it does, who sees it, and which sibling to use instead. No material gap remains.

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% — both parameters carry descriptions, including the length bound on text and the exact provenance of conversation_id. The description adds no meaning beyond the schema for either parameter, 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?

"Adds a note to a conversation" states a specific verb and resource, and the qualifier "only the team reads" pins down the exact scope. It also names the sibling it is not (postkey_send_reply), so an agent can distinguish it 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 gives an explicit when-to-use (“only the team reads”) and an explicit alternative with its selecting condition (“To answer the contact use postkey_send_reply instead”). Nothing about routing between these two siblings is left to inference.

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