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

Annotations already convey read-only, idempotent, and non-destructive behavior. The description adds 'Keyless' to clarify that no authentication is required, which is valuable operational context. It also lists the response content, partially compensating for the absence of an output schema.

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?

The description is two short sentences with no wasted words. The lookup target and returned fields are front-loaded, and the 'Keyless' note is a concise, useful addition.

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 one-parameter, read-only lookup with no output schema, this description is complete: it identifies the source platform, the input semantics, the returned fields, and the authentication requirement. Nothing critical is missing for an agent to invoke it correctly.

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?

The input schema already documents the single 'name' parameter with an example. Schema description coverage is 100%, so the baseline is 3. The description adds context by specifying 'Rust crate' and 'crates.io', but it does not materially deepen parameter semantics 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?

The description uses a specific verb and resource: 'Look up a Rust crate on crates.io', which clearly distinguishes it from sibling package lookup tools like npm_package and pypi_package. It also enumerates the exact returned fields, so an agent knows what this tool provides.

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 description clearly establishes the context for use: any time a Rust crate's metadata from crates.io is needed. It does not explicitly name alternatives or exclusions, but the platform and language are explicit enough to guide selection among package-oriented siblings.

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