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

Annotations already declare readOnly/non-destructive/closed-world, but the description adds real behavioral detail: it returns sourced facts, unknown/conflicting terms, and conditional gross-interest illustrations, and states that 'unknown terms never count as a match.' That matching rule is non-obvious and materially affects interpretation. It stops short of rate data freshness or output shape, so it is strong rather than exhaustive.

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?

Four sentences, front-loaded with the purpose, then outputs, then scope exclusions, then sibling routing. No filler or repetition; every sentence carries routing or behavioral information.

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 carries the burden of describing returns and does so at a high level (sourced facts, unknown/conflicting terms, conditional illustrations). It lacks detail on how results are shaped or when CD estimates fail (only the schema hints at exact-term matching), leaving a small gap.

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 67%, with 'state', 'product', and the two require_* flags undocumented in the schema. The description compensates by naming state, fee and direct-deposit requirements, and the savings/CD scope that maps to 'product'. It adds meaning beyond the schema for the uncovered parameters, though it does not explain 'product' as an explicit selector.

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 first sentence states a specific verb (Compare) and resource (US savings and CD APYs) plus the exact constraint set it accepts (balance, holding period, state, fee and direct-deposit requirements). It also names what it is not, distinguishing it from the lookup siblings, so an agent can route without opening a schema.

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?

Explicit routing is given: 'Use for a multi-constraint deposit comparison; use get_savings_rates/get_cd_rates for simple rate lookups.' It also states exclusions ('No eligibility decision, personalized offer, application or account opening'), covering both when-to-use and when-not-to-use.

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