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

Annotations already declare openWorldHint, idempotentHint, and destructiveHint=false, but the description adds critical context the annotations cannot: this is a paid tool ($0.001 USDC on Base or Arbitrum One) invoked by POSTing inputs as JSON to paid_url with an x402 v2 PAYMENT-SIGNATURE header. It also discloses that the result is a signed pass/fail receipt. It stops short of describing rate limits or behavior on fetch failure, 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 dense and front-loads the core purpose before alternatives, payment mechanics, and invocation details. Every sentence (price, paid URL, x402 reference) is operationally necessary for a paid tool. The fragmentary phrasing is efficient but slightly harder to parse than plain prose, which keeps it from a 5.

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?

With an output schema present, return values need not be explained, and the description correctly focuses on invocation requirements: payment protocol, price, endpoint, and sibling routing. Combined with 100% schema coverage and annotations, an agent has what it needs to call the tool. Missing only edge-case behavior (e.g., what a failing check returns), which is minor given the output schema.

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%, so every parameter is already fully documented, including defaults and constraints. The description's 'status, substring, JSON value' and 'Default status 200' merely map onto parameters the schema already explains, adding no syntax or edge-case detail beyond it. Baseline 3 applies when the schema carries the semantic load.

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 fragment 'Your conditions, one fetch: status, substring, JSON value — signed pass/fail receipt' conveys the specific action (single fetch of a URL evaluated against custom conditions returning a signed verdict), and it explicitly names the sibling alternatives (check_url_sealed for public proof, check_url_changes for watching). The telegraphic style makes it slightly less crisp than a full sentence, but an agent can distinguish it from siblings 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?

It routes explicitly to alternatives: 'Public proof: check_url_sealed. Watch: check_url_changes.' That gives clear when-to-use-this-vs-sibling guidance. It does not state exclusions or failure-mode conditions, but for a tool with two clear sibling alternatives the routing is adequate.

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