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

Annotations already establish the safe-read profile (readOnly, idempotent, non-destructive, openWorld). The description adds genuinely new behavioral facts: withheld weeks return only a reason, and the call costs $0.05 in USDC on Base via x402, which is a payment/auth precondition the annotations do not convey. Only the return shape and any rate-limiting/pagination behavior are left unstated.

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 sentences, purpose front-loaded, and the cost disclosure is placed last where it belongs. The first sentence is dense with domain jargon ('seller premiums', 'ISO week', 'first Base fill') but nothing is redundant.

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 carries the return-value burden and largely does so, describing the weekly premium series and the withheld-week behavior. It also covers the payment requirement. What is missing is any note on the currency format expectation and the practical effect of the optional platform argument on the returned rows.

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?

At 50% schema coverage, the platform parameter is documented in the schema but currency only as a regex pattern. The description usefully explains the semantic split between omitting platform (across platforms) and providing it (a single platform route), which the schema does not. However it never clarifies the currency format or that currency is required versus platform optional, so it only partially compensates.

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 names a specific resource and scope: weekly realised seller premiums against the ECB reference, per currency, per ISO week since the first Base fill. That is far more precise than a generic 'get rates', and it is clearly distinct from the liquidity_depth and paid_datasets siblings. It stops short of explicitly differentiating itself from those siblings, so a 4 rather than 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?

There is no explicit when-to-use guidance and no mention of when not to use it or which sibling to pick instead. The phrase 'one currency across platforms, or one platform route' hints at how the two arguments shape the query, but that is parameterization guidance, not usage guidance, and the agent must infer the rest.

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