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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description is free to add what they cannot: result ordering (newest first) and the returned comparison fields. It does not mention that results are capped (limit defaults to 10, max 20), so an agent may not realize the history is truncated, but the output schema covers the return 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?

Two sentences, both load-bearing: the first defines scope, ordering and payload up front, the second converts that into a recognizable user question. No redundant restatement of the tool name or title.

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 filtered-list tool with an output schema and 86% documented parameters, the description supplies everything an agent needs beyond structured fields: scope, ordering, and a motivating example. The only unmentioned detail, the result cap, is discoverable from the schema defaults.

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 description coverage is 86%, so the schema already documents region, plan, product, channel, interval and locale in detail. The description reinforces that exactly one plan and one region are addressed, which is mildly useful for understanding the required region filter, but adds no format or default details beyond the schema.

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 ("List the recorded price changes") plus tight scope ("one plan in one region") and the ordering and payload ("newest first, with the previous and new local price"). It implicitly separates itself from the feed-style sibling get_recent_price_changes via the single-plan/single-region scope, but never names that sibling, so differentiation is inferred rather than stated.

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?

The example question ("has ChatGPT Plus gotten more expensive in Brazil?") gives a concrete, recognizable use case that tells the agent what class of question this tool answers. There is no explicit when-not guidance and no named alternative such as get_recent_price_changes or compare_prices, so the agent must infer routing on its own.

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