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

Annotations already cover read-only, idempotent, open-world, non-destructive, so the safety profile is settled. The description adds real value beyond that by disclosing what the response contains — the change vs. prior business day and a month earlier, the 10y-2y and 10y-3m spreads, and an inversion flag — which matters because there is no output schema. It does not mention publication lag or data-source caveats, which keeps it short of a 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?

A single front-loaded sentence plus a short range clause; the scope (what data) comes before the boundary (how far back). Dense but zero filler, though the nested list of metrics makes it slightly harder to scan than a bulleted or two-sentence structure would be.

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 one optional parameter, full schema coverage, and no output schema, the description carries the right load: it spells out the returned fields and spreads rather than restating the schema. Only the absence of publication-timing or latency context keeps it from being fully complete for a time-sensitive data 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?

Schema description coverage is 100% and the single date parameter is fully documented, including format and lower bound, so the baseline is 3. "Today's (or any date's)" and "Any date back to 1990" loosely reinforce the default-to-latest behavior and floor that the schema already states, adding no new syntax or semantics.

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 states a concrete verb+resource ("US Treasury par yield curve") and enumerates the exact tenors and derived metrics returned, so an agent knows precisely what data it gets. It implicitly differentiates from siblings like treasury_real_yields and treasury_bill_rates by specifying nominal par yields across 1m-30y, but it never names or contrasts an alternative explicitly.

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?

Usage is only implied: the tool is for retrieving a curve snapshot for today or a historical date. There is no explicit when-to-use/when-not guidance and no routing to treasury_yield_history or the other siblings, even though one exists for historical series. An agent can infer the case but gets no exclusions.

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