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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description goes beyond them usefully by disclosing the data source characteristics (live market rates, hourly refresh) and the card-style output, which is genuine context an agent can't get from 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?

Two tight sentences, front-loaded with the action, followed by code-format and coverage details. No filler or repetition.

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 an output schema present, return values need not be explained, and the description covers scope, code format, freshness and output form. It omits edge behavior (invalid or unsupported codes, precision/rounding of converted amounts), which keeps it short of full completeness.

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 schema already documents all three parameters with examples and the 12-item cap. The description's 'ISO 4217 codes' note adds minor clarification of code format but nothing about the amount default or the max-targets limit beyond what the schema states. Baseline 3 is appropriate.

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?

States a specific verb (convert) plus resource (currency amounts), and adds scope qualifiers: live market rates, one-to-many targets, 166 currencies. No sibling tools exist to confuse it with, but the purpose is unambiguous on its own.

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?

Gives clear operative context: use ISO 4217 codes, output is an interactive card, rates are live and refreshed hourly. It does not state exclusions or failure cases (e.g., unsupported codes, stale rates), but there are no alternative tools to route against, so this is close to complete.

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