estimate_x402_cost

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

With no annotations, the description takes on the full burden and does disclose key behaviors: it does not charge ('without paying'), it checks against credit and spend-limit, and it requires an agent key. It omits possible error behavior or exact side effects, but the non-payment and auth details are well covered.

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 sentences, all informative and front-loaded: the first states action and result, the second adds policy context, the third gives sequencing and a prerequisite. No filler.

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?

For a no-output-schema preflight tool, the description explains the return value (USDC cost), the non-payment behavior, the timing, and the auth requirement. It lacks explicit error/edge-case detail, but the essential context for invoking the tool is present.

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 description does not add parameter detail beyond the schema; url and method are already documented. Baseline 3 is appropriate because the schema carries the parameter semantics.

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 uses a specific verb 'Preflight' and clearly identifies the resource (x402-protected URL) with the outcome (return USDC cost without paying). It distinguishes itself from x402_pay by explicitly stating 'without paying' and 'Use BEFORE x402_pay'.

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?

The description gives clear contextual guidance: use before x402_pay to decide gating in one round-trip, and it requires an agent key. It does not name alternative tools or negative cases, so it falls short of a 5.

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