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

Annotations already establish a safe, idempotent read, and the description adds substantial context beyond them: exact cost (0.10 USDC via x402 on Base), settlement timing (only after the analysis is computed), that the MCP tool itself is free and moves no funds, the deterministic JSON change classification and Markdown summary, and explicit limitations (no schema satisfiability/branch-overlap inference, no not or external references).

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 opening sentence is keyword-stuffed ('OpenAPI audit, API analysis, Swagger analysis, and API contract change validation') rather than front-loading the action. The single most decision-relevant fact for the caller — that this tool only validates the URL and returns payment terms, not the analysis — is buried near the end after a long paragraph on the paid analysis.

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?

An output schema exists, yet the description still covers everything an agent needs: cost and payment flow, settlement conditions, explicit capability limits, and concrete next steps (POST {"url": ...} to the returned endpoint with an x402-capable client). Nothing material for correct invocation is missing.

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% and the single url parameter is fully documented there (public OpenAPI/Swagger JSON or YAML, http/https, no credentials or query string). The description repeats the 'public OpenAPI/Swagger JSON or YAML contract' notion but adds no syntax, format, or constraint detail beyond the schema, so 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?

States a specific verb+resource (OpenAPI audit and contract change validation) and explicitly scopes it against adjacent activities ('not general OpenAPI conformance linting'). Crucially, it disambiguates what THIS call does ('validates the URL and returns the x402 endpoint and payment terms; it does not run the analysis') from the paid analysis it advertises, so an agent knows exactly what invoking check_openapi yields.

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 when-to-use context (detect breaking changes/API drift by comparing a public contract against the service's last stored snapshot, with the first check recording the baseline) and an explicit exclusion (not conformance linting). It stops short of naming the sibling compare_openapi or explaining when to prefer it over this snapshot-based check.

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