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

Annotations already cover readOnly/idempotent/non-destructive/openWorld=false, so the bar is lower. The description adds that processing is deterministic and carries a 0.002 USDC cost, which is genuinely useful pricing context not present in structured fields. It doesn't say what 'reject impossible' entails or what the output contains, but output schema exists.

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?

One dense sentence that front-loads the reject/rank/return pipeline and ends with the safety+cost qualifiers. No waste.

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?

Output schema exists, so return values needn't be explained. However, for a tool with deeply nested policy and route structures at 0% param description coverage, the description leaves the agent guessing about semantics of the filter fields, which is a meaningful gap.

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% across many nested fields (policy.* and routes.*). The description mentions 'routes' and 'policy' by name only, adding no meaning about allowed_assets, preferred_networks, max_total_atomic, or any route field. With low coverage, the description should compensate and does not.

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 action chain: reject impossible routes, rank eligible ones, return the next action. Distinguishes itself as a selector/ranker rather than a comparator or diagnoser among siblings. Does not name which sibling it replaces, so short of a 5.

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?

Implied usage: use when you have candidate x402 routes plus a policy and need the next payment action. No explicit when-to-use vs payment_preflight, payment_diagnose, or x402_quote_comparator despite this being a crowded payment-tool family.

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