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

Discloses behavioral details beyond annotations: the data source (lenders' published rate pages), that no third-party national-average benchmark is redistributed, the presence of observation timestamp and staleness status, and the restriction to factual data only. This is valuable context beyond the readOnlyHint/destructiveHint annotations provided.

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 concise yet information-dense, with the primary purpose stated upfront. Every sentence adds value: the data grouping, the loan types, the filtering instruction, the comparison constraint, and the explicit limitations. It is front-loaded with the most critical information and is appropriately sized for the tool's complexity.

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?

Given no output schema, the description explains the return structure: each rate includes note rate, APR, representative-scenario conditions, observation timestamp, source, and staleness status. It also explains the grouping behavior and the optional filtering by loan_type. This makes the tool's behavior fully predictable without additional schemas.

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 schema covers 100% of parameters with descriptive text, so the description does not need to repeat those details. It adds a small nuance about comparing only within the same loan type, but this overlaps with the schema's loan_type description. The parameter descriptions in the schema already provide adequate semantics, so the description provides minimal additional value beyond the baseline.

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 states 'Current mortgage rates grouped by loan type', providing a specific verb and resource. It distinguishes from sibling tools like get_cd_rates and get_savings_rates by focusing exclusively on mortgage rates. The mention of 'RateZip observed on lenders' own published rate pages' adds specificity beyond the title.

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?

Provides explicit usage instructions: 'Pass loan_type to filter to one; omit for all' and 'Compare only within the same loan type.' It clearly states what the tool does NOT do: 'never estimate or invite a personalized quote, imply approval, or recommend a lender.' This gives the agent clear when-to-use and when-not-to-use boundaries, even without naming siblings directly.

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