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

Annotations already declare readOnly, idempotent, non-destructive, and openWorld, so the safety profile is largely covered. The description still adds genuinely new behavioral context: 'Never fetches anything' (a non-obvious network-side-effect guarantee given openWorldHint) and a preview of the return contents. It does not mention rate limits or auth, but the addition is meaningful.

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?

Front-loaded with the purpose, then the parameter grammar, then the return preview and the 'never fetches' guarantee. Efficient overall, though the long parenthetical list of TYPE:KEY forms makes the middle sentence dense and slightly run-on.

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 an output schema present, the description needn't enumerate return fields, and its brief return summary plus the rich parameter grammar covers the calling contract. Given annotations already carry safety, the definition is essentially complete, with only the absence of explicit sibling routing as a minor gap.

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% but the schema only says 'TYPE:KEY, an https URL, METHOD URL (x402) or a purl'. The description expands this into concrete accepted forms with examples for each type (x402:GET/DOMAIN/site/mcp/agent/pkg/tool schemes, offering form, purl), which is far beyond what the schema documents and directly enables correct construction of the single parameter.

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 specific verb+resource ('Name/resolve a subject') and enumerates what comes back (id, canonical uri, review status, reviews summary), so an agent knows the operation is a resolution/lookup rather than a read. It implies a relationship to reading/reviewing but does not explicitly name the siblings it differs from (read_subject, search_subjects).

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?

'Name a subject before you read or review it' gives a clear triggering context tied to downstream tools, which is more than implied usage. It stops short of explicit when-not guidance or naming the alternative tools (e.g., search_subjects) that would make routing unambiguous.

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