List categories

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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety behavior is covered. The description adds that results include per-category server counts, but says nothing about whether the full set is always returned or whether results are cached/aggregated. With annotations carrying the behavioral load, a 3 is appropriate.

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 with zero waste, and the resource (categories) plus the return content (server counts) are front-loaded. Nothing to trim.

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 shape needn't be described, and with zero parameters and no nesting the tool is simple. The only real gap is the lack of any routing cue against directory_stats, which shares the analytical/aggregate territory.

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 schema is fully covered and no parameter guidance is needed. The description correctly implies a no-argument, whole-directory listing.

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 gives a concrete verb+resource ('List MCP directory categories') and adds the extra payload detail ('how many servers are in each'), which distinguishes it from search_mcp_servers and get_mcp_server. It does not explicitly differentiate itself from the overlapping directory_stats sibling, so it falls short of a 5.

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?

Usage is only implied: an agent can infer this is the browsing/discovery entry point for categories. There is no explicit when-to-use, no mention of when to prefer directory_stats or search_mcp_servers, and no stated prerequisites.

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