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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds the source (European Central Bank) and explicitly lists supported pairs, but does not disclose update frequency, any latency, or whether the rate is a mid-price or bid/ask. This adds some context but not substantial behavioral detail beyond 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?

The description is a single sentence followed by a compact list of supported pairs. It is front-loaded with the primary action and resource, contains no filler, and every sentence earns its place. The structure is highly scannable and efficient.

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 a single parameter, an output schema (true), and strong annotations, the description covers the essential what (current rate), source, and supported inputs. It does not mention how to retrieve historical or series data, but that is addressed via sibling tool names. For a simple read tool, the description is sufficiently complete for correct use.

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?

The input schema has 100% coverage for the 'pair' parameter, including an enum and a description with examples. The description repeats the enum values and the phrase 'G10 currency pair', which is already in the schema. It adds no additional meaning about parameter semantics or formatting beyond what the schema provides, so baseline 3 applies.

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 returns the current exchange rate for a G10 currency pair, with a specific verb ('Returns') and resource ('current exchange rate'). It distinguishes from sibling tools by emphasizing 'current', contrasting with get_fx_rate_by_date and get_fx_rate_series. The supported pairs are explicitly listed, leaving no ambiguity.

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 clearly implies this tool is for current rates, which contrasts with historical or series tools available as siblings. However, it does not explicitly name alternatives or state 'when not to use' this tool. The context signals include sibling names, so the agent can infer, but the description itself lacks direct exclusionary guidance.

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