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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds two things annotations cannot convey: the shape of the payload (total and recent download counts, latest version) and a cost of 1 credit, which is operationally important for an agent budgeting calls. It does not mention failure behavior for misspelled or nonexistent crate names.

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 sentences, zero filler, front-loaded with purpose and followed by the return contents and cost. Every clause carries distinct 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?

No output schema exists, and the description compensates by naming the returned fields, plus it discloses the credit cost. A minor gap remains around error/empty-result behavior, but for a one-parameter read-only lookup this is close to sufficient.

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?

With a single parameter and 100% schema description coverage (including the 'e.g. "serde"' example), the schema already does the documentation work. The description implies the parameter is a Rust crate name but adds no format, casing, or normalization guidance beyond that.

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 ('Get download statistics and metadata for a Rust crate') plus the exact source ('from crates.io'), which cleanly separates it from the npm_stats and pypi_stats siblings without needing to name them. The follow-up sentence enumerates the returned fields, so an agent knows precisely what it gets.

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 ecosystem binding ('Rust crate from crates.io') implicitly routes the agent away from npm_stats/pypi_stats and toward this tool when the package is a Rust crate. There are no explicit exclusions or pointers to complementary tools (e.g. package_info), so it falls short of a full when/when-not statement.

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