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

Annotations already declare readOnlyHint=true, idempotentHint=true, and openWorldHint=false, so the safety profile is covered. The description adds two pieces of genuinely new context: the sign convention ('Positive funding: longs pay shorts') and the modeling assumption ('Constant-rate scenario, not forecast'), plus it enumerates what is computed since no output schema exists. It still omits how fees are applied and whether results are netted, keeping it out of 5 territory.

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 with no filler, and the computed outputs are front-loaded ahead of the modeling caveat. The compressed, jargon-heavy style ('Caller-input...') slightly undercuts immediate readability, but nothing is wasted.

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 5-parameter calculation tool with 20% schema coverage and no output schema, the description leaves too much unspecified: units and semantics of notional_usd, how settlements map to time, whether fees are charged once or per settlement, and the units of the returned break-even. An agent could call it, but only by guessing at several inputs.

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 carries documentation. The description restates the sign convention already present in that field's schema text and says nothing about notional_usd, side, settlements, or round_trip_fee_bps (units, per-side vs round-trip application, etc.). With low coverage, the description was obligated to compensate and does not.

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 specific computed quantities — perpetual funding, fees, net carry, and linear break-even — so an agent can tell this is a funding/carry calculator rather than a pricing or stress tool. It does not differentiate itself from near-neighbors such as exit_cost, crypto_exit_check, or crypto_portfolio_stress, so it stops short of a 5. The telegraphic phrasing ('Caller-input perpetual funding, fees...') is compressed but decodable.

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 phrase 'Constant-rate scenario, not forecast' is a real usage constraint that tells the agent when this model is appropriate and what it does not do. However, there is no explicit guidance on when to choose this over siblings like exit_cost or crypto_exit_check, and no stated prerequisites or input conventions. Usage is implied rather than directed.

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