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

Beyond the readOnly/idempotent/non-destructive annotations, the description discloses real operational traits: a 300 calls/day free cap shared with HTTP free routes, a pass that lifts the cap, and a 5-minute cache that force bypasses at the cost of requiring a pass. It stops short of describing error/limit-exceeded behavior or result freshness guarantees.

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?

Rate-limit and caching context is usefully front-loaded, but the sentence then becomes a long comma-separated enumeration of returned fields. Since an output schema exists, that return-value listing duplicates structured data and dilutes the front-loaded guidance.

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, the description needn't explain return values, and it covers the key operational facts (free cap, pass, cache, force). What is missing is the sibling boundary against settled_preflight/peek, which an agent would need to select correctly among 18 tools.

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%, so all three parameters (url, pass, force) are already documented in the schema, including the header alternative and the pass requirement for force. The description largely restates the same cache/pass semantics rather than adding new meaning, 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?

The verb+resource are explicit ('Check an x402 endpoint before paying it') and the enumerated return surface makes the tool's scope concrete. It does not, however, distinguish itself from closely named siblings like settled_preflight or settled_peek, leaving an agent to infer the boundary from names alone.

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?

'Check an x402 endpoint before paying it' gives a clear usage context, and the cache/force/pass notes explain operational conditions. There is no explicit when-not or named alternative (e.g. use settled_preflight for X), so the routing decision is only implied.

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