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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, and the description adds meaningful behavioral context: this is a 'read-only metered lookup', 'misses are never billed', 'every API key carries one-off trial credit', and responseFormat changes affect context size while staying backward-compatible. No annotation contradiction exists.

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 compact and well-structured: it opens with the core purpose and evidence, then covers the format switch, billing/read-only semantics, then alternatives. Every sentence earns its place and there is no repetition or filler.

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 output schema exists, the description does not need to explain return-value structure. It fully covers the required context for a moderately complex comparison tool: scope, exact-match semantics, response formats, billing, authentication trial credit, and alternatives. The agent has enough to select and invoke this tool 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 provides full parameter descriptions, so the baseline is 3. The description adds value by clarifying that responseFormat='compact' yields tokenizer-measured context savings while the default is backward-compatible 'full', and by enumerating relevant metadata fields such as yanks, exports, module format, runtime floors, peers, and licences.

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 compares two exact published npm or PyPI versions and returns publisher-declared registry metadata changes. It is explicit about the resource (package metadata), specific verbs ('compare', 'return'), and differentiates itself from factreason_api_breaking_changes.

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 gives explicit when-to-use guidance: 'Use it for package metadata; use factreason_api_breaking_changes for a third-party HTTP API, and consult changelogs for behavioural changes.' It also clarifies metering, billing behavior, and response format trade-offs, enabling an agent to select this tool over siblings.

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