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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the description's contribution is the auth requirement and the sign-in friction, which annotations cannot express, plus what is actually counted in each mode. It does not mention rate limits, caching, or ordering of the returned ranking.

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?

Two sentences, no filler. The prerequisite is stated first, then the two output modes are contrasted in parallel 'Without X / With X' form that an agent can parse at a glance.

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?

There is no output schema, so the description shoulders return-value disclosure and does it: it names the six counted entity types and the top-20 cap. With one optional parameter and those return semantics covered, nothing needed to invoke it correctly is missing.

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% and the ISO-3166 alpha-2 format is documented there, so the schema carries format duty. The description adds the piece the schema cannot: the semantic consequence of omitting the optional parameter entirely. Baseline 3 is exceeded because the with/without distinction is genuinely behavioral meaning, not restatement.

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 concrete resource (country totals) and spells out two distinct behaviors: top 20 countries by events when `country` is omitted, and per-country counts across six entity types when it is supplied. That two-mode framing lets an agent tell it apart from generic siblings like search_events or list_leaderboards without opening the 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?

It gives explicit selection guidance for the one real decision here — omit `country` for a global top-20 ranking, supply it for a single-country breakdown — plus the prerequisite of a free Messe Atlas account. It stops short of naming any alternative sibling when a different tool would be better.

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