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

Annotations already declare readOnly, idempotent, closed-world and non-destructive, so the safety profile is covered. The description adds substantive context beyond that: that it surfaces licensing/terms decisions and robots handling, and that it takes no parameters. It stops short of describing pagination or result ordering, but for a static reference listing that is a minor omission.

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 resource and scope, followed by a purpose clause and an explicit boundary against search_kits. The parenthetical examples (Official MCP Registry CC0, Coinbase Bazaar link-out only) are dense but concretely clarify the shape of the license decisions, so they earn their space.

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?

An output schema exists, so return-value documentation is not required, yet the description still signals what kinds of facts each entry carries. With annotations covering the safety profile and usage/exclusions covered in prose, an agent has everything needed to call this correctly.

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, which is the baseline-4 case. The description reinforces this with 'no parameters,' so there is no ambiguity for the caller, though there is nothing further to specify semantically.

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?

Names a specific verb (List) and concrete resource (registries/directories ingested or excluded), plus the per-source detail returned (license/terms decision, robots handling, listing count). It explicitly separates itself from the sibling search tool, so an agent can route correctly without opening either schema.

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?

States the positive use case ('check provenance or the attribution required before citing results') and the exclusion ('it does not search listings (use search_kits)'), naming the alternative tool. Nothing about when to reach for it is left to inference.

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