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

Annotations already declare readOnlyHint, idempotentHint, non-destructive, and openWorld, so the safety profile is covered. The description adds genuinely non-obvious behavior beyond that: weekend/holiday dates silently fall back to the nearest PRIOR business day, and the response surfaces this via `used_prior_business_day_fallback`. It stops short of covering auth/rate-limit realities or output shape, keeping it at 4 rather than 5.

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?

Front-loaded with the core capability, then routing, then parameter behavior, then the alternative — a sensible order with no filler. The parenthetical aliases and trigger phrases earn their place by improving query matching, and every clause adds decision-relevant information.

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 two-parameter, read-only fetch with an output schema already present, nothing necessary is missing: the agent knows what it returns (full curve, all maturities), how dates behave, how to omit the date, and when to pick the sibling instead. Return-value structure correctly left to the output schema.

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%, and the description's date guidance (YYYY-MM-DD, omit for most recent, prior-business-day fallback) largely restates what the schema's `date` description already says. It adds no new syntax, format, or edge-case semantics for `_apiKey` beyond the schema. Baseline 3 is appropriate when the schema carries the detail.

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+resource+scope: the full US Treasury daily par yield curve for ONE date, every maturity from 1-month to 30-year in a single call. It also names the source (FRED DGS* constant-maturity series) and explicitly contrasts itself with fred_get_series, so an agent can distinguish it from siblings without opening either 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?

Gives explicit routing rules in both directions: use this when the question wants more than one maturity at once, and use fred_get_series (with a concrete example id, DGS10) when a single maturity's history over time is needed. It even lists trigger phrasings ("par yield curve", "full yield curve today/on <date>") that map user language to this tool.

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