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

Goes well beyond the readOnly/idempotent/openWorld annotations by disclosing the x402 cost (0.25 USDC on Base, eip155:8453), that the MCP tool itself is free and never executes analysis or moves funds, statelessness w.r.t. snapshot history, and unsupported reference constructs. This is exactly the extra behavioral context annotations cannot carry.

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 action and comparison semantics, then constraints, then cost. Dense but each sentence carries distinct information; only the 'purchase terms' framing adds slight ambiguity rather than waste.

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 a payment-gated, stateless comparison tool with an output schema, the description covers cost, statelessness, unsupported features, and the returned finding categories (breaking / potentially breaking / non-breaking / informational plus Markdown). An agent has everything needed to decide and call 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?

Schema description coverage is 0%, so the description must compensate. It maps the two parameters to before/after semantics and constrains them to 'public' URLs, adding a real usage constraint. It does not state whether URLs must be publicly reachable without auth or what format failures look like.

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 concrete verb and resource ('Validates explicit before and after public OpenAPI/Swagger URLs') plus the operation's nature ('immediate deterministic semantic comparison, including structural oneOf/anyOf branch changes'). It is distinguishable from a single-spec checker sibling, though the phrase 'returns purchase terms' briefly muddles whether this is an analysis tool or a payment-negotiation tool.

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?

Gives clear context and explicit exclusions: it does not infer schema satisfiability or branch overlap, and 'not' plus external references are unsupported, and it does not read or advance snapshot history. It never names or routes to the sibling check_openapi, so alternative selection is left to inference.

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