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

Annotations already provide readOnlyHint=true and destructiveHint=false, so the safety profile is clear. The description adds the scope of 'registered' instances but does not disclose pagination, ordering, or other behavioral details. Given the simple nature of the operation and strong annotation coverage, additional context is not critical, but no extra value is added beyond the scope clarification.

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?

A single sentence that is front-loaded with the action and resource, with no redundant words or filler. Every part of the description contributes directly to understanding the tool's purpose.

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?

Given zero parameters, an output schema present, and read-only annotations, the description fully covers the tool's purpose and expected behavior. No additional context is necessary for this simple list operation.

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?

There are zero parameters, so the baseline of 4 applies. The description correctly implies that the tool takes no input, and no parameter explanation is needed since the schema is empty.

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 uses a specific verb 'List' with a clear resource 'registered humanMCP instances in the marketplace'. It clearly distinguishes from siblings get_server (specific server) and search_marketplace (search) by implying a complete listing.

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?

The description implies use when one wants all instances, but does not explicitly contrast with search_marketplace or state when not to use this tool. No alternatives or exclusions are mentioned, leaving ambiguity for an agent deciding between list vs search.

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