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

Annotations already declare readOnlyHint=true, so the description is not needed to establish safety; instead it adds real substance by disclosing result scope ("every live agent owned by the account behind this key") and the exact fields returned (identity id, mosADD address, display name). It omits pagination or empty-result behavior, so it is strong rather than exhaustive.

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 sentences, both front-loaded with the highest-value information: what the list contains, then when to call it. No restatement of the tool name, no filler, and the sibling reference is packed into the first clause rather than a separate sentence.

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?

With no parameters, no output schema and only a readOnlyHint annotation, the description carries everything an agent needs: ownership scope, liveness, the three returned fields, and the follow-up call it enables. Nothing required to invoke it correctly is missing.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate — baseline 4 applies. The mention of identity id and mosADD address is useful context for the *output*, but it does not pretend to describe inputs.

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 are allowed to speak as") and immediately ties the resource to the sibling it feeds, mDM_send_as_agent. An agent can distinguish this from mDM_list, mDM_list_contacts and mAYL_list without opening any schema, because the description scopes it to agents owned by the key's account.

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 triggering condition: "Call this first when you are unsure which agent identity you hold," which is actionable ordering guidance relative to mDM_send_as_agent. It stops short of naming when *not* to call it (e.g. if the identity id is already known or comes from config), so it is clear context rather than full when/when-not coverage.

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