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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description goes beyond them by disclosing a paid cost ($0.02 USDC via x402), null-on-missing behavior, and partial-result warnings, which materially affect invocation decisions. It stops short of explaining payment/auth mechanics or latency behavior, so it is strong but not exhaustive.

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 definition is short and the core purpose plus exclusions are front-loaded before pricing and routing details. The 'When requested facts exist...' sentence is grammatically clipped and slightly awkward, but nothing is wasted.

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, so not explaining return values is acceptable, and annotations cover the safety profile. What is present (cost, null semantics, exclusions, fallback router) is enough to call the tool correctly; only routingId semantics and any payment/auth prerequisite remain unaddressed.

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 carry parameter meaning, and it only implicitly covers 'url' (public webpages) and 'fields' (requested fields). The third parameter, routingId, is never explained, and there is no hint about the field-format or count limits (1-20 fields, 120 chars) that the schema enforces without description.

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 and resource ('extracts requested fields from public webpages') and names the return shape (structured values, evidence, confidence, freshness, partial-result warnings). It also explicitly separates itself from generic web search and from already-structured sources, so an agent can distinguish it from siblings like signal_layer_router.

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 an explicit when ('requested facts exist on a public webpage but compact structured JSON is needed instead of browsing and parsing the page') and explicit when-not ('source is already structured or the task is generic web search'). It also names an alternative path (signal_layer_router for free tool selection), leaving little to inference.

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