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

Annotations already cover the safe-read profile (readOnlyHint=true, destructiveHint=false, openWorldHint=false), so the bar is lower; the description adds real value by disclosing the pricing formulas (flat per image call, per-second × duration at resolution tier) and guaranteeing the number matches what x402 would charge. It stops short of auth/permission or failure behavior for invalid model+setting combos.

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?

Two dense sentences, front-loaded with the core promise (exact price), followed by the pricing rules and the re-quote guarantee. Every clause earns its place with no 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?

With no output schema, the description correctly indicates the return is an exact USDC amount, and annotations cover safety. It is slightly thin on edge cases — unsupported model/setting combinations or whether the quote is TTL-bound relative to the later charge — but otherwise complete for a read-only pricing tool.

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 83%, so the schema already carries most parameter meaning and the baseline is 3. The description adds an interaction the schema doesn't spell out — duration and resolution jointly drive video pricing — though it leaves aspectRatio and the payer discount interplay to the schema.

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 — 'Exact USDC price for a model+settings combo' — plus the scope ('before paying'), so an agent knows this is a pre-flight pricing lookup, not a generation call. No sibling overlaps this capability, making the distinction unambiguous.

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?

'before paying' implies the usage context, and the note that the x402 endpoint re-quotes from the body hints that this is a preview. But there is no explicit when-to-use statement, no prerequisite (e.g. must have modelId from list_models), and no named alternative — routing guidance is left to inference.

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