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

Goes well beyond the annotations by disclosing that the tool is paid ($0.25 USDC on Base or Arbitrum One), requires an x402 v2 PAYMENT-SIGNATURE header, posts inputs to a specific paid URL, and produces a signed receipt from a single fetch. These are material invocation and payment details the annotations do not provide.

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 description is compact and front-loads the proof purpose before naming the alternative and payment mechanics. It is dense with necessary technical terms, though the opening phrase is more marketing-like than direct.

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?

Given an output schema exists, the description need not explain the receipt structure. It covers the fixed condition, alternative tool, payment protocol, cost, endpoint, and invocation method, leaving no major gap for an agent 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 description coverage is 100%, and the schema already fully explains both url and idempotency_key, including redirects, timeout, body cap, and replay behavior. The description adds call mechanics but no parameter meaning beyond the schema, 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 capability: prove a URL was live at a given moment by fetching once and sealing the transcript in a signed receipt, with HTTP 200 fixed as the condition. It also names check_url_custom for custom conditions, so the agent can distinguish it from the sibling 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 says to use check_url_custom instead when the caller wants their own conditions, and the fixed HTTP 200 scope makes the default use case clear. It does not mention other siblings such as check_url_changes, so it is not fully exhaustive.

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