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 real value by disclosing provenance ('daily comparison of official homepage records'), which tells the agent how fresh the data is, but it says nothing about return shape, pagination, or what happens when no changes are found.

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 sentence that front-loads the time window and resource, then the returned fields, then provenance. No filler, though the embedded defaults/max duplicate the schema rather than earning their place.

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 an 8-parameter read tool with no output schema, the description does sketch the returned fields (changed date, before/after price), which partly compensates. But it leaves the direction/limit interaction, empty-result behavior, and the overlap with plan_price_history unexplained.

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 88%, so the schema already documents nearly every parameter, including the days range and default. The description merely restates 'N days (default 7, max 60)' and adds no syntax or interpretation 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+resource: plans whose monthly fee rose or fell within the last N days, plus the changed date and before/after prices. Clear on its own, but it never distinguishes itself from the sibling plan_price_history, which sounds closely related.

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 when-to-use guidance, no exclusions, and no routing to alternatives such as plan_price_history or price_index. The only clarifying sentence explains data provenance (daily homepage comparison), not usage conditions.

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