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

Annotations already declare read-only, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds genuinely new behavioral context: the call is free, rate-limited, returns coarse/cached data, and performs no fresh probe — all of which affect how an agent should treat the result.

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?

Two terse sentences with zero filler; the cost/rate-limit caveat and the cached-data scoping constraint are both front-loaded. Every fragment earns its place.

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-value detail is not required. For a single-parameter read tool, the description supplies the essential caveats (free, rate-limited, coarse, no fresh probe); only an explicit pointer to the probing alternative is missing.

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?

With one parameter at 100% schema description coverage, the schema already documents the required URL and even gives a format example, so the baseline is 3. The description restates 'one x402 endpoint URL' but adds no syntax or format detail beyond the schema.

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 ('Peek') and resource ('one x402 endpoint URL') and specifies what is returned: coarse status and a quality score. The parenthetical '(no fresh probe)' implicitly separates it from a probing sibling, though the distinguishing sibling is not named.

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?

'Free, rate-limited' and 'no fresh probe' imply the conditions that favor this tool (cheap, cached lookup) over a probing alternative, but no sibling is named and no explicit when-not is stated. Usage is implied rather than spelled out.

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