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

Annotations already indicate readOnly, idempotent, and non-destructive behavior. The description adds valuable operational details: free quota, per-IP rate limiting, shared quota with demo routes, midnight UTC reset, and paid alternatives. This goes beyond the annotations without contradicting them.

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 concise and well-structured: the first sentence states the core purpose and outputs, the second provides usage constraints and a paid alternative. No unnecessary words, and important information is front-loaded.

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?

Given the presence of an output schema, the description does not need to detail the return format, and it appropriately covers rate limits and paid routes. The description explains the diff and classification outputs, which is sufficient for an agent to decide whether to use the tool. Minor gaps like version format and explicit sibling differentiation prevent a perfect score.

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 has 0% description coverage, so the description must compensate. It mentions 'two pinned versions of one package,' which implies from_version and to_version, but it does not explicitly define each parameter or mention the ecosystem enum. The parameter names are self-explanatory, giving some semantic help, but the description could have added more detail (e.g., version format, accepted ecosystems).

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 clearly states the tool's function: it produces a symbol-level diff between two pinned versions of a package, listing added/removed/changed signatures, new deprecations, and a breaking/additive/neutral classification. This is specific, uses a clear verb and resource, and distinguishes itself from sibling tools that check existence or signatures rather than comparing versions.

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 provides clear context about usage constraints: free with a 25-calls/day limit shared with demo routes and a paid alternative for higher volume. However, it does not explicitly mention when to use this tool versus the sibling tools (e.g., for single-symbol lookups), leaving that to the agent to infer from the purpose.

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