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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is covered. The description adds the FRED source and 'no payment required' context, but does not disclose response format, pagination, or rate limits. It does not contradict annotations, but adds minimal behavioral depth beyond them.

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 sentences, with the first front-loading the core function and the second providing usage guidance. No wasted words, ideal length for the tool's simplicity.

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 zero parameters, an output schema, and strong annotations, the description fully covers the necessary context: what is returned, from where, and how it differs from related tools. Nothing essential 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?

The tool has zero parameters and the schema has 100% coverage (vacuously). Baseline for 0 params is 4. The description correctly does not attempt to explain parameters since there are none.

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 a specific verb ('Returns'), resource ('most recent 30-year US Treasury constant maturity yield'), and data source ('FRED'), even specifying the series code (DGS30). It distinguishes from siblings by explicitly directing users with different needs to get_current_value or get_series.

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 explicitly says 'For other series use get_current_value or get_series', providing direct guidance on when to use this tool versus alternatives. It also notes 'Free — no payment required', a practical contextual guideline.

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