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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description usefully adds output ordering ('latest months first') and a usage disclaimer, but says nothing about data source, publication lag, or value units/format despite having no output schema.

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?

Three short sentences, front-loaded with the core resource before the ordering note and disclaimer; nothing is wasted. Minor deduction for the choppy fragment structure ('Latest months first.') rather than flowing prose.

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 single-parameter read-only tool with no output schema, the description covers what data is returned, its granularity (monthly average), instrument coverage, and ordering. Only detail that would help an agent interpret results, such as units or publication lag, is missing.

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% for the single 'months' parameter (default 3, min 1, max 24), so the schema already does the explanatory work. The description's 'latest months first' only weakly reinforces the recency semantics and adds no syntax or format detail beyond the schema.

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?

Names a specific resource (monthly average interest rates on US Treasury marketable securities) and enumerates the covered instrument types (bills, notes, bonds, TIPS, FRNs). The domain-specific scope clearly separates it from sibling rate tools like ecb_key_rates and fx_rate_ecb without needing to open any 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?

'Latest months first' and the instrument enumeration imply this is a lookup for US Treasury yields, which is adequate implied usage. However, there is no explicit when-to-use, no guidance on choosing it over the similar-looking ECB/FX rate siblings, and 'Data only, not advice' is a disclaimer rather than usage guidance.

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