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

With no annotations, the description carries the full burden and discloses important behavioral context: the data comes from exchange public market-data APIs, there is a free preflight sample, and calls cost $0.01 USDC on Base via x402 payment in params._meta. It does not mention rate limits, historical window, or response shape, but the payment and data-source transparency is strong.

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?

The description is front-loaded with the core purpose, followed by pricing, payment, and endpoint details. It is dense but every sentence adds operational value for an agent that must know cost and access mechanics.

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 one-parameter tool with no output schema, the description covers purpose, source, and payment well. However, it leaves ambiguity about what 'history' means (time range, granularity) and what the response contains beyond funding rates and annualized carry, which an agent may need before relying on it.

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 coverage is 100%, and the single symbol parameter is already documented in the schema as an asset symbol. The description adds a small amount of context by naming BTC, ETH, and SOL as supported examples, but provides no additional parameter syntax or constraints beyond the schema.

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 (perpetual-futures funding rates and annualized carry) and scope (BTC, ETH, SOL and more, one call). It is clear what the tool returns, but it does not explicitly distinguish itself from siblings like funding_rates__rates, funding_rates__batch, or fundinglens__rates.

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?

The description mentions a free /preflight sample and pricing, but gives no guidance on when to use this tool instead of sibling funding-rate tools such as funding_rates__batch or funding_rates__best. No exclusions or alternative-selection criteria are provided.

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