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

Beyond the readOnlyHint/openWorldHint annotations, the description discloses the 500-link cap and, critically, the payment model: $0.002 USDC on Base per call via x402, with unpaid calls returning PaymentRequired and x402 clients paying automatically. That cost/auth behavior is exactly the operational context an agent cannot infer from annotations or schema.

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?

Three tight sentences: output content first, then use case, then cost. Nothing is redundant and the most decision-relevant facts are front-loaded.

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 two-parameter read-only extraction tool with no output schema, the description covers what comes back (URLs, anchor text, internal/external), the volume limit, the intended use, and the payment requirement. 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?

Schema coverage is 100%, with both parameters documented, including the only/exclude enum, so the baseline is 3. The description's 'internal vs external' phrasing corroborates the external filter's meaning but adds no format, default, or edge-case detail beyond what the schema already says.

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 precisely what the tool returns: every unique outgoing link on a web page, including absolute URLs, anchor text, and the internal/external split, capped at 500. That is far more specific than the title '/v1/url/links', though it never names a sibling (url_metadata, url_to_markdown, url_check) to differentiate itself explicitly.

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?

It gives a clear positive use case: 'Use it to crawl a site or find related pages,' which tells an agent the intended scenario. There is no when-not guidance or routing to the adjacent url_* siblings, so it stops short of full alternative coverage.

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