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

With no annotations, the description carries the full burden and does so well: it declares the operation read-only, states the cost ($0.003 USDC on Base via x402), constrains the timing to pre-signing, and enumerates what it does NOT do (URI binding, signature verification, nonce-state verification, settlement or delivery proof) – a strong, honest capability boundary.

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?

Front-loaded with the critical 'PRE-SIGNING ONLY' constraint and densely packed with actionable content. Mostly earns its place, though the cost is stated twice (parenthetical '$0.003' and trailing 'Costs $0.003 USDC'), a minor redundancy.

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 nested-object tool with no annotations and no output schema, the description covers purpose, scope, cost and limitations well. However it never explains what the preview actually returns (a pass/fail, a metadata comparison result?), and the 'payment'/'challenge' inputs are undefined, so an agent still lacks the information to interpret results or construct those objects.

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 0%, so the description must compensate. It meaningfully maps the intent fields ('payee allowlist, resource URL and max spend'), but the 'payment' and 'challenge' top-level objects remain completely opaque in both schema and description, leaving half the parameter surface undocumented.

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 – a 'read-only x402 v2 Base USDC payment-intent preview check' that 'Compares untrusted envelope metadata'. The 'PRE-SIGNING ONLY' scope and the explicit limitation list distinguish it from the sibling x402-payment-diagnostic without naming it directly.

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?

Gives clear context for use ('PRE-SIGNING ONLY') and what to supply, plus explicit exclusions (never send private keys, signed headers or raw signatures). It stops short of routing the agent between this and the sibling diagnostics tool, so the alternative-selection guidance is implied rather than explicit.

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