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

Annotations cover the safety profile (readOnlyHint, openWorldHint=false), and the description adds meaningful behavior: 'Free', 'Input provenance is not verified', the actual/365 day-count with a 28-32 day range, and the disclaimer that the spread establishes neither fees nor causality. These are real traits 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?

The key scope statement is front-loaded and the remainder is a tight sequence of short caveat sentences. Dense but generally economical, with each sentence carrying a distinct constraint.

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 no output schema, the description hints at the return ('The spread') and supplies the domain caveats an agent needs to interpret it. It is nearly complete, only omitting an explicit statement of the response shape and any sibling routing.

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 both parameters (snapshot, benchmark) are already fully documented, including constraints like positive start/end values and the us_treasury_total_return_index kind. The description adds only the 'identical dates' and caller-supplied framing, so 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?

The description states a specific verb (arithmetic comparison) and both resources precisely: a saved measured USD instrument response versus caller-supplied US Treasury total-return index levels. This is clearly distinguishable from siblings like compare_rwa_snapshots and compare_settlement_costs.

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 gives explicit applicability constraints (identical dates, 28-32 day window, USD only) and clear exclusions (spot rates, unmatched windows, quoted yields, other currencies are not comparable). It stops short of naming an alternative sibling tool to route to, but the when/when-not framing is strong.

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