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

Annotations already declare readOnly, idempotent, non-destructive and open-world behavior, so the safety profile is covered. The description adds genuinely new behavioral context: a per-call price of $0.02 USDC via x402, which affects whether an agent should call it at all. It still omits rate limits, latency, and failure/empty-result behavior, keeping it short of a 5.

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 with the primary selection condition front-loaded, followed by exclusions and cost. Every sentence carries information. It loses a point because the lead sentence is an incomplete clause with no verb, which slightly obscures the purpose it is meant to front-load.

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 return values need not be described, and the description adequately covers selection criteria and cost. However, with three parameters at 0% schema description coverage, an agent cannot determine what `fields` should contain or what `routingId` is for; that gap is not compensated anywhere.

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% across all three parameters, so the description carries the full burden. It only loosely implies `url` ("public webpage") and `fields` ("requested facts"), and says nothing about `fields` being a list of up to 20 names of at most 120 characters, nor anything about `routingId` — which is entirely unexplained anywhere.

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 frames the tool as a condition ("When requested facts exist on a public webpage but compact structured JSON is needed") rather than stating an explicit verb+resource like "extract named fields from a URL." The resource (a public webpage) and output (compact structured JSON) are discernible, but the action itself is only implied. It never states plainly what the tool does, so an agent must infer it from the title.

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 explicit negative selection criteria ("Do NOT use when: The source is already structured or the task is generic web search") and an escalation path ("call signal_layer_router first for free"). This is exactly the when/when-not/alternative routing an agent needs, and it names a real sibling.

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