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

Annotations declare readOnlyHint=true, so the safety profile is already covered; the description adds valuable context by specifying the returned fields (id, subject, entry count, field semantics) and the fixed nine-deck scope, implying a small, stable result set. It stops short of stating that the catalog is static or whether results are paginated, which keeps it below a 5.

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 catalog contents and return fields are front-loaded in two sentences, with the sequencing directive ('Call this before search_deck') placed last where it reads as an action. No filler or repetition of the tool name as an explanation.

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 input parameters, no output schema, and only a readOnlyHint annotation, the description carries the remaining burden itself and does so: it explains what the tool returns and how its output feeds other tools. Nothing an agent needs in order to call it correctly or interpret the result 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?

The tool takes zero parameters, so there is no parameter ambiguity to resolve and the baseline is 4. The description wisely spends its space on the output shape instead of inventing parameter guidance.

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 ('The catalog of K2 study decks') and enumerates the exact scope (nine decks: kanji, HSK, Hangul, Spanish, French, Latin, medical Latin, birds). It also describes the return payload (deck id, subject, entry count, field meanings), which separates it cleanly from search_deck and get_entry.

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 instructs 'Call this before search_deck,' giving a concrete ordering rule relative to a named sibling. It also notes the deck id is 'the value other tools take,' clarifying the handoff to downstream tools rather than leaving the agent to infer it.

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