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

Annotations already declare readOnlyHint=true, idempotentHint=true and non-open-world, so the safety profile is covered. The description contributes real behavioral context beyond that: the 8-hour averaging window, that values are percentages, and that they are aggregated across exchanges. It omits the observation horizon (the 30-day series only appears in the schema) and whether the result is a single figure or a time series.

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 compact sentence with the core attribute (8-hour average, %, per coin, cross-exchange) front-loaded and no filler. Nothing is wasted and nothing essential to identifying the metric is buried.

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 and one optional parameter, the bar is modest, but the description leaves the return shape ambiguous: 'average' suggests a scalar while the schema's parameter text implies a 30-day series. For a simple read-only lookup this is adequate but not fully self-sufficient.

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 the single enum parameter documents its own meaning, including the BTC default and the 30-day series scope. The description's 'per coin' merely echoes the schema and adds no format or default detail, 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 names a specific resource (8-hour funding rate of perpetual futures) and qualifies it precisely: averaged, in percent, per coin, across exchanges. A verb is only implied, but no sibling tool covers funding data, so there is no ambiguity about what this tool retrieves.

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 statement of when to use this tool, when not to, or what alternative to reach for; the description is purely a data summary. An agent must infer that this is the tool for funding-rate requests solely from the name and title.

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