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

Annotations already declare readOnlyHint=false, openWorldHint=true and idempotentHint=true. The description adds behavior beyond that: drafts (especially file drafts) require human browser review, and a queued result signals queued transport rather than recipient approval or reading — genuinely useful operational context an agent could not derive from the annotations.

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?

Four dense sentences, each earning its place, with the core action and precondition front-loaded before the caveats. No filler or repetition.

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?

An output schema exists, so return-value documentation is not required, and the description still supplies the non-obvious semantics of the queued result and the human-review requirement. Coverage is essentially complete for a 3-parameter tool with a full schema.

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 schema fully documents connection_id, content blocks and idempotency_key. The description only lightly reinforces the idempotency-key reuse rule already stated in 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 (Prepare/draft) plus resource (text or private attachment blocks) and a scoping precondition (an accepted connection). It does not explicitly contrast with the adjacent siblings messages.send or federation.messages.status, so the boundary between drafting and sending is left partly to inference.

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 real operating guidance — reuse the idempotency key only with identical content, and note that pending/file drafts require human browser review. However it never says when to choose this tool over messages.send or federation.messages.status, so the alternative-selection guidance is only implied.

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