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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the safety profile is covered. The description adds genuinely useful behavior beyond that: authoritative source with no estimates, no API key needed, and a refresh cadence of once per US business day (stale-data expectation).

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?

Dense and front-loaded: source, scope, and derived fields come first, then invocation facts. Every clause carries information; 'No args' is slightly redundant with the empty schema but still useful in a routing context.

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: full curve range, day-over-day changes, spread pairs, and inversion state. Combined with the no-key and update-frequency notes, an agent has everything needed to call and interpret this tool.

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?

Zero parameters, so the baseline is 4; the explicit 'No args' matches the empty schema and removes any doubt about required inputs. There is no parameter surface that needs further explanation.

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?

States a specific verb and resource: a US Treasury daily par yield curve snapshot from treasury.gov. Names the exact scope (1M-30Y), derived metrics (10Y-2Y, 10Y-3M spreads, inversion state), and clearly differs from siblings like get_fx_rates or get_fundamentals.

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?

Conveys practical invocation facts ('No args', 'Free public data, no key', daily update), which helps an agent decide it can call it cheaply. But it never states when to prefer this over alternatives or when it is not appropriate, leaving usage to inference.

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