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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds genuinely new behavioral context: the decomposition logic (inputs + residual margins/demand/supply) and the plan-tier requirement, which annotations cannot express. It stops short of describing the response shape or latency.

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 motivating question, then a single dense sentence covering periods, decomposition mechanics, and examples. Every clause earns its place, though the inline examples make it slightly heavy for a two-parameter 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?

For a read-only, closed-world explanation tool with no output schema, the description conveys what the answer conceptually contains (attribution across inputs plus residual) and the access tier. Nothing essential to 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 50%: 'code' is documented with examples and a search_indices cross-reference, but 'period' has an enum and default with no schema description. The description recovers part of that gap by enumerating the periods (1w/1m/3m/6m/1y), but adds no meaning to 'code' beyond the schema. Baseline 3 for partial coverage.

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 verb+resource ('Explain a price move') and then defines exactly what the explanation is: a decomposition of the change into input moves and residual factors, with concrete examples (PP ← propylene, gas, power). This is distinctive enough to separate it from data-fetching siblings like get_index_history or get_index_forecast, though it never names an alternative explicitly.

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 by the framing question 'Why did a price move?' and the plan gate ('Essential plan and above'), which tells the agent who can call it. However, there is no explicit when-to-use/when-not guidance and no pointer to alternatives such as get_index_history or get_market_movers for related questions.

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