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

With annotations only declaring readOnlyHint=false and destructiveHint=false, the description adds real behavioral context: a direct conversation is created on first use (a side effect not visible in the schema), messages are stored permanently, delivery is live-push with inbox as fallback, and receipts are tracked. This is exactly the delivery/persistence semantics an agent needs before writing.

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 tight sentences, each carrying new information: what it does, how to target, then delivery/persistence behavior and the receipts alternative. Nothing is repeated from the schema 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?

An output schema exists, so return values need not be described, and the write-side behavior is well covered. Minor gaps remain around mutual exclusivity of peer_ref and conv_key and how group conversations are addressed, but nothing that would cause a wrong 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 0%, so the description must carry the load, and it does explain the two meaningful parameters functionally (peer_ref creates a direct conversation, conv_key continues one). It leaves gaps: what happens if both or neither are supplied explicitly (peer_ref default null, conv_key default null), and no format expectations for body.

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?

Opens with a specific verb plus resource and scope: "Send a message in a conversation (1:1 or group)". This immediately separates it from read-oriented siblings such as list_messages, list_conversations, and get_message_receipts.

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 an explicit routing rule between the two targeting modes: peer_ref for messaging a colleague versus conv_key to continue an existing conversation. It also names the alternative tool for delivery status (get_message_receipts), so an agent knows where to go for the adjacent need.

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