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

Beyond the readOnlyHint/openWorldHint annotations, the description discloses a genuinely important behavioral trait: this is a pay-per-call tool billed in x402 USDC on Base, and the response returns a payment challenge when payment is absent. That is exactly the kind of cost/auth behavior an agent must know before calling. It stops short of describing pagination or rate limits, so not a 5.

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 tight sentences with zero filler. The capability statement is front-loaded and the payment caveat follows immediately, so the most decision-relevant facts land first.

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 a full output schema present, return values need no explanation, and the schema covers all parameters. The one omission is sibling differentiation from 'funding', but the payment-flow disclosure makes this definition complete enough to invoke correctly.

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 100% and all three parameters (days, symbol, exchange) are documented with defaults and ranges in the schema itself. The description adds only the 'up to 90 days' ceiling, which duplicates the schema's '1-90' range, so the baseline 3 applies.

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 states a specific resource and scope: multi-exchange funding rate history up to 90 days. It is clear what the tool returns, but it never distinguishes itself from the sibling 'funding' tool, which an agent would reasonably consider an alternative for funding-rate data.

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 when-to-use, when-not-to-use, or alternative-tool guidance. The closest thing to routing information is the 90-day scope, which merely restates a parameter constraint rather than telling the agent when this tool is the right pick over 'funding'.

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