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

Annotations already declare this a read-only, idempotent, open-world read, so the safety profile is covered. Beyond that, the description discloses non-obvious behavior: the candidate universe is capped at the 300 most-traded open markets, settling/live-game markets are filtered out, and the returned fields are enumerated (old/current price, pp move, 24h volume, slug). It stops short of covering pagination or rate limits, but the exclusions and universe cap are genuinely useful context.

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 dense paragraph, but front-loaded with the triggering user questions before the mechanics, and every sentence carries information (universe, fields, exclusions, sibling handoff). The middle clause listing return fields is slightly overloaded but still earns its place given there is no output schema.

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 compensates by enumerating the returned fields and their interpretation, plus the market universe, the exclusion rules and the default volume floor implied by 'most-traded'. An agent has everything needed to call this correctly and interpret the result.

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 100%, so the schema already documents all five parameters including defaults and ranges, making 3 the baseline. The description echoes window/direction/include_games semantics and implies the min-volume behavior via '300 most-traded', but adds no syntax or edge-case detail beyond the schema text for limit, window, direction or min_volume_24h_usd.

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 ('Ranks the 300 most-traded open markets by price change') with the exact scope of the ranking, and differentiates itself from pm_flow, which is positioned as the follow-up tool for attribution. An agent can select this over pm_book, pm_market or pm_flow without opening any schema.

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?

Opens with an explicit trigger list ('what is moving, trending or changing... what moved overnight or this week... biggest gainers and losers') and names the alternative for drill-down ('pm_flow shows who moved it'). It also states the negative case: settling markets and live sports games are excluded unless include_games is true.

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