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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds minor context by mentioning 'source policy' as part of the returned data, but it does not disclose other behavioral traits such as pagination, rate limits, or potential incompleteness of the list. The score reflects that the description adds some value but does not significantly go 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, well-structured sentence that front-loads the verb 'List' and immediately conveys the tool's purpose, scope, and usage timing. Every word earns its place, with no redundancy or filler.

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?

This is a simple list tool with no parameters, an output schema present, and annotations covering safety. The description provides the essential workflow context ('before requesting a pair-specific intraday reference-rate series') and clearly states what is listed. Given the tool's simplicity and the structured metadata, the description is fully complete for an agent to use it correctly.

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 tool has zero parameters, and the schema is empty. According to guidelines, a 0-parameter tool receives a baseline of 4. The description does not need to explain any parameter semantics, and the 'source policy' mention hints at what the output contains, which is adequate.

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 uses the specific verb 'List' and clearly identifies the resource: 'public official FX reference-rate sources and their source policy.' It also distinguishes itself from sibling tools like fx_intraday_reference_rates by explicitly noting 'before requesting a pair-specific intraday reference-rate series,' making the tool's purpose unambiguous and differentiated.

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 clear usage context by stating 'before requesting a pair-specific intraday reference-rate series,' which tells the agent when to invoke this tool. However, it does not explicitly name alternative tools or provide exclusion criteria, so it falls short of a full 5. The guidance is strong but could be more direct about 'use this instead of X'.

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