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

Annotations already declare this as a read-only, idempotent, non-destructive, closed-world operation, so the safety profile is covered. The description adds real behavioral content beyond that: it aggregates all legs on one underlying, surfaces breakevens and best/worst outcomes, and frames results as deterministic arithmetic. It does not state behavior when the range is omitted or when there are no positions.

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 tightly written sentences, both front-loaded with the core capability and its scope. Every clause — including the closing 'Arithmetic, not a forecast' — carries information and nothing is redundant.

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 three-parameter tool with no output schema, the description adequately covers what is returned (P&L curve, breakevens, best/worst in range), which is the main thing the missing output schema would otherwise require. The remaining gap is default-range behavior when low/high are omitted.

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 67%, and the schema's own text for low/high is thin ('Optional low price'), while symbol is undocumented. The description clarifies that the range drives the P&L sweep, but never explains what range is used when low/high are null, nor that symbol identifies the single underlying being evaluated.

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 gives a specific verb and resource — computing P&L at expiry for one underlying — and explicitly scopes it to 'shares plus every option leg' plus breakevens and best/worst outcome. This clearly distinguishes it from siblings like my_option_positions, my_portfolio, or my_option_expirations, which report holdings or dates rather than payoff.

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 clearly implied: use it when the user wants payoff-at-expiry arithmetic for everything held on a single underlying. 'Arithmetic, not a forecast' usefully heads off expectations of prediction. However, it names no alternatives and does not say what happens if the user holds nothing on that symbol, so it stops short of explicit when/when-not guidance.

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