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

Annotations only declare open-world, non-idempotent, non-destructive behavior; the description adds substantially more: $0.05 pricing, x402 payment handshake details including the _meta['x402/payment'] retry, an automatic refund intent on failed delivery, coverage limits (~57% of issues, 20-40% of WCAG criteria), and 90-day free report retrieval. This is exactly the kind of context structured fields 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 purpose and return shape, then limitations, then payment mechanics — a sensible ordering. It is long and repeats the x402 story in two places ('price RULED' and the parenthetical MCP/HTTP note), costing it a point, but nearly every sentence carries operational information.

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?

No output schema exists, so the description must describe returns — and it does fully: verdict-first summary, per-finding fields, capped samples, incomplete checks surfaced, and report_id retention. Combined with the payment and preflight instructions, an agent has everything needed to call it 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?

Single required parameter with 100% schema description coverage; the schema already documents the http/https-only, ports 80/443, no-private/loopback/credentialed-URL constraints. The description adds no further meaning about the url argument beyond payment metadata, so the 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 ('Accessibility findings for one page from automated checks in a real headless browser') and scopes it to a single page, which implicitly separates it from the access_crawl sibling. An agent can tell what it does and what it does not cover without opening the schema.

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?

Explicitly prescribes sequencing ('Call access_scan_preflight first to check servability and price for free') and sets boundaries ('Findings only; automated checks cover a subset'). It does not name access_crawl as the alternative for multi-page work, so the routing guidance is inferred rather than stated.

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