Calculate perpetual funding and fee drag

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

Annotations already declare readOnlyHint/idempotentHint/openWorldHint=false, so the safe-pure-function profile is established. The description adds the modeling assumption ('constant-rate scenario, not forecast'), which is genuine value, but the funding sign convention it states duplicates the schema's parameter description, so the incremental disclosure is modest.

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?

Two short sentences, front-loaded with the computed outputs before the assumption caveat. No filler, though the telegraphic style ('Caller-input perpetual funding, fees, net carry and linear break-even') reads as a fragment rather than a sentence.

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?

There is no output schema, and while the description names the outputs (net carry, break-even) it never explains their shape, units, or sign conventions. For a calculator with 5 inputs at 20% schema coverage, a caller still lacks enough to interpret the result with confidence.

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 only 20% — only rate_bps_per_settlement is documented — so the description carries an extra burden. It loosely maps to some inputs (funding/rate, round-trip fees) and clarifies side via the sign convention, but notional_usd, settlements, and the fee default/units are left unaddressed.

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 concrete computed quantities (perpetual funding, fees, net carry, linear break-even), which is specific enough to distinguish it from siblings like exit_cost or crypto_portfolio_stress. It lacks an explicit verb ('calculate' only lives in the title) and the phrase 'Caller-input' is jargon, but the resource and scope are unambiguous.

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?

'Constant-rate scenario, not forecast' and 'Caller-input' imply when the tool applies (you supply the rate; no live-data fetch, no forecasting), which is a usable boundary. However, no alternative sibling is named and there is no explicit when-not-to-use statement or prerequisite list, so routing relies on inference.

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