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

Annotations already declare idempotent, non-destructive, open-world, but not read-only; the description adds the genuinely non-obvious behavioral fact that this call is metered and requires an x402 / X-Bazaar-Key payment of 0.01 USDC. It does not explain the result shape or how invalid SemVer input is handled, which keeps it below 5.

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?

A single sentence that leads with the payment/access precondition and then the purpose — both load-bearing. Slightly front-loaded with the paid-call bracket, but nothing is wasted.

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 one-input, no-output-schema tool the description covers purpose and cost, and implicitly describes the return value as one of three classifications. It leaves the missing 'target' parameter's required-ness and invalid-input behavior unstated, which matters given the schema is incomplete.

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 schema documents only 'current' (and marks nothing required, with additionalProperties true), yet the description reveals that a second input, 'target', is expected. That is real value beyond the structured fields, though it does not say whether target is required or what format validation 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 specific verb (compare), a specific resource (two SemVer strings, current vs target) and the actual result taxonomy (major breaking / minor compatible / patch). No sibling tool does version comparison, so it is trivially distinguishable from the linter/calc siblings.

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?

Usage is only implied by the name and the 'current vs target' phrasing; there is no statement of when to prefer this over a plain diff or a package-manager resolution, and no exclusions. An agent can infer the use case but gets no routing guidance.

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