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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint false. The description adds value by disclosing the null return case ('when there is no recorded history') and listing the output fields. However, the phrase 'currently-displayed cheapest offer' is ambiguous—it could depend on user context, which is a minor gap.

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?

The description is two efficient sentences. The first sentence front-loads the key output fields, and the second provides the usage intent. Every word earns its place; no redundancy or fluff.

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?

Given that an output schema exists (not shown but indicated), the description adequately covers the return values. It explicitly mentions the output fields and the null-case behavior. The only minor gap is clarifying 'currently-displayed,' but overall it is complete for a read-only trend tool.

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?

The input schema has 100% description coverage, so the schema already fully documents each parameter. The description does not add additional meaning or constraints beyond what the schema provides, meeting the baseline expectation.

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 clearly states what the tool does: returns price history data (window min/max, current price, % drop, floor, raw points) for the cheapest offer of an audiobook. It also provides a concrete use case ('is this a good price right now / has it dropped?'), distinguishing it from siblings like get_price_index which likely covers broader indices.

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 description explicitly tells when to use the tool ('Use to answer...'), giving clear context. It does not list when not to use or mention alternatives, but the use case is specific enough to differentiate from siblings.

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