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

Annotations already declare readOnly/IDEMPOTENT/openWorld/non-destructive, so the safety profile is covered. The description adds genuinely useful non-annotation context: the authentication requirement (Carry Oracle key) and the retention property of the data source (beyond the 500 h window). It stops short of describing rate limits or pagination, hence a 4 rather than 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?

Three tight sentences, no filler, with the data scope and the 'beyond 500 h' constraint front-loaded ahead of the alternative-tool routing. Slightly dense but every clause carries information.

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?

For a two-parameter read tool with no output schema, the description covers what is needed to call it correctly: coin format, hourly granularity, retention window, auth requirement, and the sibling to use instead. Return-field specifics are implied by the enumerated metrics but never laid out, which is the only minor 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 100%, so the baseline is 3. The description's mention of the HIP-3 prefix convention (xyz:NBIS) and the hourly granularity restates what the schema already documents for coin and hours, adding no new syntax or format detail.

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 (retrieves) and resource (hourly funding/premium/mark/OI/volume for one coin) with an explicit scope qualifier: history retained beyond Hyperliquid's 500 h window. It also names the sibling it is not, so an agent can distinguish it from carry_funding_matrix without opening either schema.

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?

Gives both the when-to-use condition ('one coin's hourly history beyond 500 h') and the alternative with its selecting condition ('for the current snapshot of all coins use carry_funding_matrix'). The key prerequisite ('Requires a Carry Oracle key') is stated up front, leaving nothing to inference.

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