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

Annotations already cover safety (readOnlyHint, destructiveHint=false, openWorldHint) and steak the idempotency profile; the description adds the commercial behavior not present in structured fields: $0.003/call, first 25 free, failed calls free, and that repeats are charged. It also restates that the tool changes nothing, consistent with readOnlyHint. It stops short of describing response shape or error behavior, but the pricing disclosure is the materially useful addition.

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 returned fields, then the usage moment, then pricing. Every sentence serves the agent's decision, though the pricing/call-charging sentence is slightly long and could be tightened without losing meaning.

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?

With no output schema, the description carries the burden of describing return values, and it does so by enumerating the exact fields returned. Combined with the annotations covering safety and the single fully-documented parameter, an agent has everything needed to call and interpret this tool.

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 100% for the single required parameter, so the schema already defines `package`. The description's example (package=requests) gives a modest hint about expected value format, but adds little beyond that, so the baseline 3 applies.

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 precise resource and enumerates exactly what is retrieved: latest version, summary, licence, required Python version, home page, release date and release count for a PyPI package. That is specific enough to distinguish it from the nearest sibling, npm_downloads, without opening either schema.

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?

"Use to check a dependency before installing it" gives a clear triggering context, and the worked example (package=requests) shows the call shape. There is no explicit when-not guidance or named alternative, but for a one-param lookup tool the intended moment of use is unambiguous.

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