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

Annotations already indicate readOnlyHint=true (safe read operation) and destructiveHint=false. The description adds valuable behavioral context: it explains the estimation nature, clarifies that both quotes use the same guard rate to isolate tenor effect, and breaks down the cost components. No contradiction.

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 well-structured, front-loading purpose and behavior before usage. It is slightly verbose but every sentence adds value. Could be trimmed slightly, but overall concise for the complexity.

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?

Given the tool has 6 parameters, no output schema, and no enums, the description provides comprehensive coverage: it explains the estimation logic, usage scenario, and behavioral nuance about the guard rate. The return breakdown is described, which compensates for the missing output schema.

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 baseline is 3. The description adds value by explaining the relationship between parameters and the calculation (e.g., feeDifference, guardSpreadCost, extensionMargin) and context for the dates. However, it does not elaborate on individual parameter semantics beyond what's in 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 clearly states the tool's purpose: 'Get an indicative price for extending a Guard to a later settlement date.' It distinguishes itself from sibling tools like 'price_guard' by explicitly describing the extension scenario and referencing the formula breakdown.

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 provides explicit usage guidelines: 'Use this when a customer asks "how much would it cost to extend my Guard by X months?"' and notes that parameters match price_guard plus dates, clearly indicating when to use this tool vs alternatives.

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