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

Annotations already indicate read-only and non-destructive behavior. The description adds that the differential may be 'stored or derived' and that the result includes metadata (measure, rate type, curve family, tenor), which is useful for interpreting the response and goes beyond 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 focused sentences with no filler. The core purpose is stated first, and the guidance about returned metadata is kept minimal and relevant.

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?

The tool has 11 parameters and an output schema, and the description covers the essential purpose and result interpretation. Some relationships between parameters (e.g., curve_family only relevant for forward) are left to the schema, but overall this is adequate for a read-only query tool.

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?

All 11 parameters have detailed descriptions in the schema, so the description adds little beyond mentioning that returned metadata should be used. There is no additional parameter-specific semantics beyond what the schema already provides.

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 identifies the action ('Return') and the resource ('stored or derived rate differential for one FX pair'). This distinguishes it from sibling tools like rate_curve and policy_rate_differential_visual_artifact, which focus on curves or visual outputs.

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 implies usage for retrieving FX pair differentials and instructs using the returned metadata when explaining results, but it does not explicitly state when to use this tool over alternatives or provide exclusions. Usage context is largely implicit.

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