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

Annotations already declare readOnlyHint and idempotentHint, so safety is covered. The description adds the plan gating ('Essential plan and above') which is genuinely useful behavioral context, but says nothing about result ordering, limits, or response shape.

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?

One dense sentence front-loads the core function then tacks on period and group modifiers. No wasted words, though the parenthetical layer definitions and group examples make it slightly cramped.

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 ranking tool with no output schema, the description covers scope, layers, periods, and plan gating. It omits tie-breaking/ordering, the meaning of limit per direction, and default period behavior, so an agent still infers call shape from the schema.

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 only 25%, but the description carries the meaning of layer, period, and group ('optionally within a group (e.g. polymer, fibre, energy)'). It does not explain period semantics as windows for the ranking or what limit counts, leaving some gaps unbounded by either schema or description.

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+resource ('Biggest risers and fallers among inputs (L0), raw materials (L1) and semi-finished (L2)') with the material layers it covers, distinguishing it from generic price tools like get_prices or get_live_index.

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?

No when-to-use guidance or naming of alternatives. It mentions 'Essential plan and above' as an access restriction, but does not route an agent to get_prices, explain_price_move, or get_index_history for adjacent needs.

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