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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is fully covered. The description's added value is disclosing the payload contents (change, median, series) in the absence of an output schema, but it says nothing about units, currency, granularity, or how the series is ordered.

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 clause with the resource front-loaded and no filler; every phrase (chain-linked, group scope, 30-day change, median, series) carries information.

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 zero-required-parameter, read-only aggregate lookup with no output schema, the description gives the essential shape of the answer (change, median, series). It falls short only on the 'since' window semantics and the default group, which an agent calling with no arguments would need.

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% ('group' has no description, 'since' only says YYYY-MM-DD). The description partially compensates by glossing the group enum as 'CN, US or all models', but it omits any meaning for 'since' (window start? cutoff?) and does not state the default group when the parameter is omitted.

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 concrete resource (a chain-linked LLM price index) and enumerates what it reports: 30-day change, median price and series. It is more precise than the bare name, though it never explicitly contrasts itself with siblings like list_llm_prices or list_price_changes, so the agent must infer the distinction from 'index' vs 'prices'.

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 explicit when-to-use or when-not-to-use statement, and no alternative is named. Usage is only implied by the vocabulary: an 'index ... series' with a '30-day change' suggests trend/aggregate analysis rather than per-model lookups, which overlaps with list_price_changes.

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