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

Annotations already establish readOnlyHint=true, so the safety profile is covered; the description goes further by disclosing the universe rules (preferred/class shares and TOKYO PRO Market excluded, tokyoPro parameter flips that), the absence of a market-cap floor, that results are limited to the latest trading day, that changes are split-adjusted decimals, and the 10-token cost. It stops short of describing the shape of the returned ranking entries, which would be the remaining useful detail given there is no output schema.

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 definition is front-loaded with the resource and its three modes, then layers universe rules and formatting conventions in compact clauses. It is dense but mostly earns its words; the duplicated Japanese restatement of the first sentence adds length without new information, and the trailing 'Costs 10 tokens' would read better grouped with the other operational constraints.

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?

For a read-only, zero-required-parameter ranking tool with a well-described schema and no output schema, the description covers everything needed to call it correctly: what is ranked, over what time window, which securities are in scope, how filters interact, and what the numeric output means. Nothing material for correct invocation 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 80%, so the baseline is 3, but the description earns above that by clarifying semantics the schema leaves ambiguous: 'actives' means largest trading value, the market parameter's omit-behavior versus tokyoPro, the common-stock-only default that governs includeEtf, and the decimal convention for reported changes. It does not address the limit bounds (1–100), which the schema handles silently.

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 specific resource and scope: top movers of the latest trading day in Japan, with the three modes (gainers = largest rise, losers = largest fall, actives = largest trading value) defined inline. It is clearly distinguishable in intent, but it never names or contrasts with close siblings such as get_rankings, get_new_highs_lows, or get_sector_performance, so an agent must infer the boundary.

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 through the filtering capabilities (TSE 33-sector or market segment) and the universe definition (common stocks only, no market-cap floor), which help an agent decide whether the tool fits a given request. However, there is no explicit when-to-use / when-not-to-use guidance or routing to an alternative tool for historical rankings or per-stock quotes.

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