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

With no annotations, the description carries full burden and excels. It discloses the live probe, ~8s timeout, expected HTTP 402 response with parseable payment body, price conversion to USDC, address format/checksum checks, network mainnet vs testnet, flagging of dead/cold/zombie endpoints and price traps, and the signed verdict format. It even explains the 'sign facts, not judgments' principle. No annotation contradiction.

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 description is long but information-dense and front-loaded with the main purpose in the first clause. Each subsequent detail (checks, return format, pricing) serves a functional role. The 'Sign facts, not judgments' phrase is a bit stylistic but adds transparency. It earns its place, though somewhat verbose compared to the leanest examples.

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?

Given the tool's complexity (multiple checks, output verdict, safety-critical), the description is remarkably complete. It explains the return value (OK/WARN/AVOID plus flags), covers edge cases (decoy, dead endpoints, price traps), includes pricing, and clarifies the verification principles. No output schema exists, so the description must explain return values, which it does.

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 baseline is 3. The description mentions the timeout ('~8s timeout') which aligns with the timeout_seconds parameter and default, but does not add substantial meaning beyond the schema. The url parameter is self-evident. No additional syntax or format details are provided that would elevate above baseline.

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 opens with 'Preflight safety check for an x402-gated endpoint, BEFORE you pay it,' which is a specific verb ('preflight'), a clear resource (x402-gated endpoint), and a clear scope (safety check before payment). It distinguishes from siblings by focusing on x402 endpoints and payment preflight, not generic transactions or payments.

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 provides clear context: use this tool before paying an x402 endpoint. It explicitly says 'BEFORE you pay it,' which tells the agent when to invoke it. It does not name alternative tools or exclusions, but the x402-specific scope and the timing are sufficient guidance for this context.

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