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

With no annotations, the description carries the full burden and does well: it discloses the cost ($0.01 USDC/call), the protocol and chain (x402, eip155:8453), that the probe request is unpaid (non-destructive), and the red-flag signal it returns. It does not cover failure modes or what happens when no 402 is returned.

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?

A single dense sentence, front-loaded with cost and protocol tag, then purpose, then output fields. 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?

There is no output schema, and the description effectively compensates by enumerating the decoded offer fields, so an agent knows what to expect back. For a two-parameter probe with no annotations, the only missing piece is error/edge-case behavior.

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% and both parameters (url, method) are documented in-schema. The description implies the URL is a paid endpoint and that a single request is made, but adds no syntax or format detail 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 verb and resource: 'Pre-payment check of an x402 endpoint' that makes 'one unpaid request' and decodes the 402 offer. The decoded field list (network, USDC or not, USD price, payTo, testnet, red flags) makes it clearly distinct from siblings like verify_usdc_payment and mcp_probe.

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?

'Pre-payment check' gives a clear usage context: run this before committing funds to an endpoint. It does not explicitly name alternatives or exclusions (e.g., when to follow up with verify_usdc_payment), 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.