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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered elsewhere. The description adds one genuinely useful behavioral fact – that the chance-of-profit figure requires IV and days – but says nothing about how contracts scale the outputs or how optional inputs degrade the result. Modest added value above the annotations.

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?

A single sentence, front-loaded with the instrument type, then a tight enumeration of outputs. Because there is no output schema, every listed metric earns its place rather than being redundant. No filler or hedging.

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 no output schema, the description correctly compensates by naming the returned figures. The conditional requirement for IV and days is also disclosed. What is missing is any routing against the debit_spread sibling and any note on how the contracts parameter changes profit/loss totals, leaving a small gap for an 8-parameter tool.

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%, so the baseline is 3; the description earns extra by tying iv_pct and days together as the joint precondition for the modeled chance of profit, which the schema documents only individually. It adds no guidance on credit sign conventions or contract scaling, but that pairing is real added meaning 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 names the exact instrument (bull put / bear call credit spread) and enumerates the computed outputs – width, max profit/loss, breakeven, return on risk, credit-to-width, chance of profit. An agent can distinguish this from debit_spread purely from the name and first clause. It stops short of explicitly contrasting itself with the debit_spread sibling, so it is clear but not fully differentiating.

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?

Usage is only implied: it is a calculator for credit spreads, and the clause 'when implied volatility and days are given' hints that the probability output is conditional on supplying those two optional args. There is no statement of when to pick this over debit_spread, no prerequisites, and no exclusions, so the guidance is thin.

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