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 return shape (total, latest day, average) plus null handling for uncollected days. However it says nothing about auth requirements, rate limits, error behavior, or whether the 100-day cap is a hard limit — the safety/operational profile is thin.

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 the verb and resource, followed by output detail and then a use case — no filler sentences. Slightly dense with clauses packed via dashes, but every clause carries 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?

For a simple 2-parameter read tool with an output schema present, the description covers purpose, when-to-use, and key result semantics. The main gap is that parameter-level meaning is left entirely to the schema.

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 0%, so the description would need to compensate, but neither `package` nor `days` is explained directly. It implies a 100-day ceiling through 'up to 100 days' and the schema supplies the days default, so the self-evident parameter names carry most of the load.

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 — 'Fetch daily download counts for an npm package' — with scope details (up to 100 days). The 'npm' qualifier implicitly separates it from the sibling get_pypi_trends, but it never names or contrasts that sibling explicitly.

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?

Provides a when-to-use trigger ('Use when the user asks how an npm package is growing'), which is useful but narrow. No when-not conditions, no mention of get_pypi_trends or get_package_comparison as alternatives for adjacent questions, so routing relies on inference.

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