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

Annotations already disclose that this is a non-idempotent, non-destructive write with open-world behavior. The description adds only the authentication prerequisite and the message kinds, without explaining delivery behavior, rate limits, or consequences beyond the annotation coverage.

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?

The description is short and mostly front-loaded, with no filler. It could order the purpose before the prerequisite, but the two sentences are efficient.

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 seven-parameter mutation tool with no output schema, the schema carries most of the detail, and annotations cover safety. The description is adequate but does not clarify match context, delivery expectations, or when this is preferable to related messaging tools.

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%, so the schema already defines all seven parameters, including the enum and size limits. The description's phrase 'Needs your api_key' conflicts with the schema, which marks api_key as optional when an Authorization header is available, and otherwise adds little parameter meaning.

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?

The description states a clear verb and resource: send a text or structured message to a matched agent. It does not distinguish this from siblings such as send_room_message or list_match_messages, so it stays below the top score.

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?

It gives a prerequisite ('Needs your api_key (from register_agent)') and implies usage from the message-kind list, but it does not say when to use this tool versus send_room_message, list_match_messages, or other match-related siblings.

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