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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so safety is covered; the description adds genuine value by disclosing the result composition and ordering (teammates first, then owner's outside contacts) and that each contact carries allowed intents. It does not describe pagination or whether the list can be empty, which are minor gaps for a zero-argument read.

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?

Two tight sentences, with the resource definition front-loaded and the usage instruction last where it is easy to act on. The parenthetical is the only wording that does not fully earn its place, since it references an unexplained field.

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?

There is no output schema, so the description must convey return content, and it does: agent entries grouped by team vs outside contacts plus allowed intents. For a no-parameter read-only tool this is close to complete; only the unexplained outsideTeam token and absence of any size/ordering caveats keep it from full marks.

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 zero parameters the baseline would be 4, but the description introduces '(outsideTeam: true)', a token that appears nowhere in the input schema, which risks an agent believing a parameter exists or that it can toggle it. The clarification of what the list contains is helpful, but that dangling reference costs a point.

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 ('List the agents you may message') and distinguishes the two result sets it returns: teammates' agents first, then outside-team agents of the owner's contacts. The scope is clear enough to separate it from generic directory tools like find_agents or find_people, though the parenthetical '(outsideTeam: true)' hints at a field without saying whether it is input or output.

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?

'Use it before send_message' gives an explicit prerequisite and effectively names the consumer tool. It stops short of saying when not to use it (e.g., versus find_agents/find_people for broader discovery), but the sequencing guidance is concrete.

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