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

Beyond the readOnly/openWorld annotations, it discloses provenance and freshness: each rate was read from the provider's own page on the date returned. That is meaningful data-quality context an agent cannot get from annotations. It does not describe result shape, ranking ties, or how stale rates are handled.

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 tightly written sentences: the scope and provenance come first, the trigger phrases last. Every clause carries information and nothing is repeated.

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?

For a two-parameter read-only lookup with full schema coverage this is close to sufficient, and the provenance sentence covers the main trust question. With no output schema, the exact fields returned and the meaning of 'date returned' remain unstated.

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 coverage is 100%, so both parameters are already documented and the baseline applies. The description's kind list mirrors the enum but omits 'annuity', which is actually a valid enum value, so it adds no meaning and introduces a minor inconsistency.

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 names a specific resource (highest verified U.S. cash rates) and enumerates the categories covered, so an agent can immediately tell what comes back. It stops short of distinguishing itself from siblings like get_sweep_rate and get_treasury_yields, which overlap with the 'sweep' and 'treasury' kinds it lists.

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 quoted example intents ('best savings rate', 'best money market fund', 'where should I keep cash') give concrete routing signals for when to call it. There is no stated when-not-to-use case and no pointer to the sibling tools an agent should prefer for single-category lookups.

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