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

With no annotations, the description carries the full behavioral burden, and it does disclose the return content (dated snapshots of monthly price and billing terms), which implies a read operation. However it says nothing about permission requirements, how far back the history goes, snapshot count, or pagination, leaving notable behavioral gaps for a zero-annotation tool.

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 tight sentences: purpose and output shape front-loaded, then the dependency for obtaining the input. No filler or redundancy.

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 single-parameter read tool with no output schema, the description adequately covers what it does and what it returns, compensating somewhat for the missing output schema. It could be more complete by noting the history's coverage window or any rate/recency constraints.

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?

There is only one parameter and schema coverage is 100%, so the schema already documents plan_id with an example. The description reinforces that it takes a single plan id but adds no format or constraint detail beyond the schema, making the baseline 3 appropriate.

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 ('Pricing changes over time for one BillWatch plan') and immediately clarifies the return shape ('dated snapshots of the listed monthly price and billing terms'). It is clearly distinguishable from the sibling search_deals, which is named as the id-lookup path rather than a competitor for this data.

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?

Explicitly routes the agent to search_deals to obtain the required plan_id, which is real actionable guidance for the one input. It does not, however, state when this tool should be used versus not used (e.g., recency limits or scope exclusions), so guidance is clear but not exhaustive.

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