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

Annotations already declare readOnlyHint and openWorldHint, and the description adds substantial operational context beyond them: an exact price ($0.002 in USDC per successful call), the payment rail (x402 on Base, Solana or Arc), and the billing rule that failed calls are free. It also discloses uneven per-exchange coverage (only Bybit supplies open interest and long/short ratio), which sets correct expectations for the response.

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 sentences, each front-loaded with the most decision-relevant facts (what it returns, what it is not, what it costs). No filler and no repetition of the schema or title.

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?

An output schema exists, so return values need not be re-explained; the description nonetheless covers the important edge cases (per-exchange field asymmetry, no history) and the x402 payment requirement. Nothing an agent needs to call or budget for the call is missing.

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 sole parameter (symbol) is fully documented with format and default in the schema. The description only reinforces that the rate is 'for one coin' and adds nothing on ticker syntax or the USDT-margined constraint at the parameter level, so baseline 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 verb and resource (current perpetual-futures funding rate for one coin across Binance, OKX, Bybit) and enumerates the returned fields (annualised rate, mark price, Bybit open interest and long/short ratio). It explicitly disambiguates against the misleading 'heatmap' name by stating it is a table of exchanges, not a time-series heatmap.

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?

It clearly scopes applicability: one coin at a time, current snapshot only, and explicitly excludes funding history. That tells the agent when not to use it, though it does not name a specific alternative sibling (e.g. for historical funding or multi-coin scans) the way a top-tier definition would.

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