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

With zero annotations the description carries the full burden and does so well: it discloses the exact price and chain ($0.02 USDC on Solana per pair), the billing unit (one report per pair), that documents are processed in memory and never stored, and that a paid retry re-sends both documents. It also bounds the result explicitly ('not a safe to upgrade certification'), which prevents over-trust in the output.

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?

It is a single dense run-on of three long sentences with stacked subordinate clauses, and the actual purpose arrives after the price. Front-loading cost is defensible for a paid tool, but the 'processed in memory only and never stored' clause is repeated in the schema and the middle sentence carries too many clauses at once.

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 paid, mutable-effect tool with no output schema, the description covers cost, privacy, retry behavior, scope limits, and roughly what the report contains. What is missing is payment mechanics (how the USDC charge is authorized) and failure/refund behavior, which an agent needs before committing funds.

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%, so the schema already documents version_a, version_b, and the pairs array including their mutual exclusivity and accepted formats. The description adds only the charging semantics for pairs and the retry-resends-both behavior, which is marginal beyond the structured fields. 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?

The description states a concrete resource: a signed breaking-change diff report for one pair of submitted documents, with per-token counts and located removed/added/changed findings under breaking-change-diff/v1 rules. That is far more specific than a restatement of the name. It never names the sibling tools (apidiff_precheck, apidiff_criteria) that an agent would likely weigh it against, so it stops short of a 5.

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 is implied rather than directed: the price is front-loaded and the closing sentence excludes a 'safe to upgrade' certification as an intended use. However, no alternative tool is named and there is no instruction to run apidiff_precheck first, despite that sibling clearly existing in the same family. An agent can infer this is the paid, final diff step, but must infer it.

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