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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered structurally. The description adds only that the messages are between the agent and the human; it says nothing about ordering, pagination, freshness, or what a message record contains.

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 a single short sentence with no wasted words and the human-channel concept is front-loaded. However, its brevity comes at the cost of not stating the core list/retrieve operation, so it is terse rather than optimally structured.

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 list tool with no output schema and an ambiguous name, the description should clarify scope, ordering, and return shape. It provides none of that, leaving the agent to infer the read behavior entirely from annotations and the sibling list.

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 single optional api_key parameter is fully documented in the schema (100% coverage), including the exact auth fallback case. The description adds no parameter semantics beyond that, so the schema is doing the work and 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?

The description restates the resource named by the tool ('messages') but never supplies a verb such as 'list' or 'retrieve'. It adds only the channel ('between you and the human'), so an agent must infer the actual operation from the tool name.

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?

There is no guidance on when to call list_messages versus send_message, contact_human, or any other sibling. The description neither names alternatives nor states conditions for use.

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