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

Annotations already declare readOnlyHint and idempotentHint, so the safety profile is covered. The description adds value with an inline example of the returned structure (unique_servers plus by_status), which is important given there is no output schema, but it says nothing about whether counts are cached, how fresh the snapshot is, or whether transport/package breakdowns are always present.

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?

Three short sentences: what it returns with its split dimensions, a sample payload, then the call constraint and the motivating question. Nothing is repeated and the most decision-relevant content (the breakdown categories and example output) comes first.

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 no-argument aggregate tool with no output schema, the description supplies the missing return-shape information via an example payload and enumerates the split dimensions, so an agent knows exactly what it will get and whether it answers the question.

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?

Zero parameters, so there is nothing for the description to disambiguate beyond confirming 'No arguments', which it does. Baseline 4 applies for a genuinely argument-free tool.

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?

States a specific verb and resource ('Returns how many MCP servers the Official MCP Registry lists') and enumerates the exact breakdown dimensions (status, remote transport, package type). The scope as a whole-registry snapshot implicitly contrasts with new_servers_count_since and daily_new_counts, but no sibling is named explicitly.

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?

'Good for "How many MCP servers are there, and how many run remotely?"' gives a concrete usage scenario, and 'No arguments' makes the call frictionless. There is no explicit when-not or named alternative, so the agent must infer that time-series/novelty questions belong to the sibling count tools.

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