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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds valuable context beyond these: 'No authentication required,' the default behavior of returning only Live-country currencies, and the exact counts (~130 entries). It does not cover rate limits or pagination, but for a read-only list tool this is sufficient.

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 front-loaded with the core purpose and then packs in necessary details. The dash-separated clauses make it slightly run-on, but every clause contributes meaning—no fluff. It's compact enough for the information it conveys.

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 simple list tool with one optional parameter, the description covers everything needed: purpose, default behavior, return fields (code, name, symbol, decimal places, zero-decimal flag, min/max amounts), and how to apply the results. There is no output schema, but the description compensates fully. No gaps remain.

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 100% with a clear description for the includeAll parameter. The tool description adds further nuance by quantifying the default response ('typically a handful') versus the full list (~130 entries), reinforcing the parameter's effect 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 opens with 'List supported (Stripe-compatible) ISO 4217 currencies' — a specific verb and resource. It further distinguishes itself from sibling list tools (e.g., list_countries) by explicitly noting its purpose for payoutCurrency, making the tool's role unmistakable.

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?

It provides clear downstream usage: 'Use minPayoutAmount as the floor when setting dispatch_physical_task.payoutAmount.' It also explains the default vs. includeAll modes. However, it does not explicitly name alternative tools or state when not to use this tool, so it misses a full 5.

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