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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description contributes genuinely new behavioral context: the tool functions without authentication and degrades to free-tier session limits, which an agent needs to interpret the response scope.

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, front-loaded with the primary return content, with the auth caveat tucked into a parenthetical. Nothing is redundant and nothing is missing.

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 detail is not the description's burden, and the tool takes no arguments. For a simple read-only introspection tool, the description supplies everything needed to invoke it correctly, including the keyless case.

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; the baseline for a no-param tool is 4. The description correctly does not invent parameter discussion.

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 names the exact resource and contents returned — the caller's plan, limits, and today's per-limit-group usage — with a specific verb-resource reading ('usage'). No sibling tool in the namespace (fetch, get_article, search_news, etc.) overlaps, so the agent can route to it unambiguously.

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 implied rather than stated: the agent infers 'call this to check your quota.' The parenthetical does give a real condition — it works without a key and then reports the free MCP session's limits — but there is no explicit when-to-use/when-not versus alternatives, 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.