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

Annotations only cover read-only and open-world; the description adds substantial operational context beyond them: unlisted venues are omitted and reported in 'unavailable', rates are as published by venues, funding is paid between traders not to the venue, data is information-only, and the call costs $0.002 USDC via x402 with failures not charged. Cost, failure behavior and edge-case handling are all disclosed.

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?

Front-loaded with the returned fields, then edge cases, then pricing — a sensible ordering with no redundant sentences. It is on the long side and the 'not financial advice' line is boilerplate, but every other sentence 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?

With an output schema present, return values need no explanation, and the description still covers coverage gaps (unavailable venues), data provenance, and billing. The only missing piece is explicit routing guidance versus sibling tools like crypto_price or perps_markets.

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 is documented with format and examples ('2 to 10 letters or digits, e.g. BTC, ETH or SOL'). The description only restates 'one coin' without adding format or venue-specific ticker conventions, so 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?

States a specific verb+resource (perpetual futures funding for one coin) and enumerates exactly what is returned: funding rate, interval, annualised rate, next funding time, open interest in coins/USD, mark or oracle price. It also names the four venues, so an agent can distinguish it from crypto_price (spot) or perps_markets (market listings) without opening the 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?

Scope is clear (one coin, funding data, multi-venue), which implies the use case, but there is no explicit when-to-use or when-not statement and no sibling named as an alternative. The agent must infer that this is the funding-specific tool rather than e.g. crypto_price or perps_markets.

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