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

Annotations cover the write/safety profile (readOnly=false, idempotent=false, destructive=false), and the description adds real substance on top: the once-per-round call contract, the 'unknown' rating's next-day rescheduling effect, and the fact that results include next due dates and learned status. It stops short of covering failure behavior, permission requirements, or what happens on a duplicate call (relevant given idempotentHint=false).

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?

Front-loaded with the core purpose, then usage rules, then rating semantics, then returns — a sensible order. Most sentences earn their place, though the 'never offer a round that is not recorded' clause drifts into product policy that is only loosely tied to invoking this tool.

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 usefully describes the return value (next due date and learned status at 21+ days). Combined with the call-frequency contract and rating semantics, an agent has enough to invoke correctly; only error handling and the id format are unaddressed.

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 0%, and the description compensates well by explaining the rating semantics ('known' only without a hint; 'unknown' brings the word back the next day) and that the array must carry every word asked. It does not explain the id field constraints (1-64 chars) or the 100-item cap, so a small gap remains.

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 first sentence gives a concrete verb and resource: 'Saves a quiz round to the user's spaced-repetition schedule.' This is clearly distinguishable from siblings like add_vocabulary_items, save_deck, or list_due_words, which handle vocabulary/deck management rather than recording round results.

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?

Explicitly states when to call ('once at the end of every round with every word asked, not after each word') and pre-empts a likely misuse case (practice rounds with mode 'all' still need recording). It even warns against offering an unrecorded round, which is a behavioral rule an agent could not infer elsewhere.

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