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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety bar is lower. The description still adds substantive semantics: the 7% threshold, the two-day holding rule, the 26-week lookback limit, and the included Guide link, though it says nothing about result volume or ordering.

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 what it returns, with the optional parameter explained last in a compact clause. The single long sentence is dense but every clause (thresholds, hold period, fields, default) carries decision-relevant 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?

With no output schema, the description does the work of describing the return contents (store, was/now, percent, day last read, Guide link), which is what an agent needs. It omits ordering, volume, and whether empty weeks return an empty payload, leaving minor gaps.

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 100%, so baseline is 3, but the description adds meaning beyond the schema: 'week' is the LAST day of the requested week, and the lookback is capped at 26 weeks back. That boundary constraint appears nowhere in the input 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?

The description names a specific verb and resource: 'the week's changes in iDevice's records,' then enumerates the three change classes it returns (price moves, release window changes, launches/stage changes). This clearly separates it from siblings like whats_coming (forward-looking) and get_price_history (single-product history).

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?

It establishes clear use context — a weekly digest of only material changes (≥7% moves held two days) with a stated default window. It never names an alternative tool or an explicit when-not condition, so it stops short of full routing guidance.

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