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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is covered. The description goes well beyond that by defining 'away' (>30 s), the groups buckets (<=1/<=3/<=5/<=10/<=20 s and '20+'), and how the server uses median time to distinguish quick from slow answers — genuinely useful semantics for interpreting results.

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?

The content is dense but front-loaded: the field inventory comes first, followed by definitions of the trickier fields. Nearly every clause earns its place, though the closing sentence on review-interval mechanics is more internals than an agent strictly needs.

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?

With no output schema, the description must describe the return shape, and it does so thoroughly, naming each top-level field and the structure of times[skill]. For a single-parameter read-only tool this covers what an agent needs to call and interpret it.

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?

There is one parameter (term) with 0% schema description coverage, so the description must carry meaning. It implies term is the vocabulary word being queried, which is adequate but adds no syntax, case-sensitivity, or lookup-failure guidance beyond that inference.

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 specific verb (returns statistics) for a specific resource (a vocabulary word) and enumerates the returned content: status, skills levels, known marks, and quiz answer times. It is clearly distinguishable from generic siblings like progress or profile, though it never names a sibling explicitly to route against.

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?

There is no statement of when to reach for word_stats versus progress, quiz_history, or vocab_list. The only framing sentence, 'For discussion only', comments on how the server interprets timing data rather than when to call the tool.

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