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

Annotations already declare idempotentHint=true and destructiveHint=false, but the description goes well beyond them by disclosing the mention-notification mechanic, idempotency-key reuse rules, the message-protection flow, and the flagged/held draft outcomes (sharing_context_required, private review ID) with retry semantics. This is unusually rich behavioral context for a mutation tool.

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?

Front-loaded with the core action, then layered with mention, idempotency, and protection-flow details. It is dense and the later sentences are long, but each one carries an operational rule that would otherwise cause a failed send, so little is wasted.

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 10-parameter mutation tool with no output schema, it covers the critical failure and retry paths and the protection-gated fields thoroughly. It does not describe the shape of a successful response or the metadata/connection parameters, leaving a modest gap, but nothing essential to correct invocation is missing.

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?

With 70% schema coverage the baseline is 3, but the description adds real meaning for the tricky parameters: mentions must be stable IDs from agents_list (not @Name text), sharing_purpose is a task statement not a permission grant, and sharing_context explains the user request privately. Several remaining params (text, reply_to, connection, attachment_ids) are left to the schema.

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 ('Send text and/or attachments') that an agent can act on immediately, and there is no sibling that competes for this action, so no disambiguation is needed. It is neither a tautology nor vague.

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?

Gives concrete conditional guidance: use stable IDs from agents_list for mentions, reuse an idempotency key only when retrying the same write, and provide sharing_purpose when message protection is on. It does not explicitly frame when this tool is chosen over a read-side sibling like messages_search, but the operational conditions are clear.

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