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

Beyond the annotations (readOnlyHint, openWorldHint, idempotentHint), the description adds meaningful behavioral context: no auth or API key required, no PII, idempotent and safe to retry, public endpoint rate limits, and detailed meta.available handling with retry guidance. It also warns against reporting unavailable data as zero, which is valuable operational behavior not captured in 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 description is dense but well-structured: a one-sentence summary, followed by usage guidance, then behavior and response-shape details. Every sentence adds operational value, and the most important scoping information is front-loaded. Despite its length, nothing feels redundant given the no-parameter, output-rich nature of the tool.

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 no-argument tool with an output schema and annotations, the description is fully complete: it names all return series, explains units, warns that series have different observation dates, documents the result envelope, and explains how to handle meta.available=false. An agent has everything needed to call the tool and interpret the result correctly.

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 tool has zero parameters, so the baseline is 4. The description explicitly states 'No arguments' and the input schema confirms an empty properties object, leaving no ambiguity about how to invoke the tool.

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 opens with a specific, resource-rich statement: 'Latest U.S. mortgage rates, TBA par coupons, Treasury and SOFR benchmarks, and mtgmon's fitted MBS basis in one call.' It also distinguishes itself from sibling tools by explicitly naming get_loan_performance as the alternative for GSE loan performance. An agent can confidently know what this tool returns and what it does not.

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 provides explicit 'Use for' and 'Do not use for' sections, listing concrete example queries such as 'what are mortgage rates today' and naming get_loan_performance as the alternative for GSE loan performance. This gives an agent clear selection criteria with no inference required.

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