msg_send

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

With no annotations to lean on, the description still discloses the non-obvious behavioral trait that governs this tool: delivery is pull-only, so the recipient will not be notified. It omits return-value behavior, failure modes (e.g. unknown recipient), and whether messages can be edited or recalled.

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 with the purpose front-loaded and delivery semantics before addressing details. The final sentence largely repeats the schema's own "to" description, costing a little efficiency.

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 simple messaging tool with no annotations and no output schema, the description covers purpose, delivery model, and addressing adequately. It leaves minor gaps around return value and recipient-existence behavior that an agent might want.

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 are already documented, including the "to" = name or "all" convention. The description merely restates the "to" semantics and adds no syntax, format, or constraint beyond 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+resource ('Leave a message for another Claude window (shared mailbox)') and immediately distinguishes itself from the pull-based siblings by noting the recipient only sees it via msg_read. An agent can tell this apart from msg_read/msg_board 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?

Clearly frames the asynchronous delivery model ('nothing is pushed') and explains the addressing convention, which tells the agent when this communication channel is appropriate. It stops short of explicit when-not guidance or naming msg_board as the alternative for browsable notes (that hint lives only in the schema).

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