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

Annotations already declare read-only, idempotent, non-destructive behavior, so the safety profile is covered. The description adds genuinely non-obvious context: the call costs $0.35 USDC via x402 on Base or Solana, which materially affects an agent's decision to use a bundle rather than cheap single calls. It omits data freshness/latency, which keeps it from 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?

Two sentences, both earning their place: the first front-loads contents and the routing rule, the second front-loads the cost constraint. The dense ticker list is functional precision rather than padding.

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 explaining the return value, and it does so by naming every field and computed spread. It stops short of describing the response envelope (units, timestamps, nesting), leaving a modest gap for a data-returning 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?

The tool takes zero parameters, so the baseline is 4; there is nothing for the schema to document and nothing the description needs to disambiguate. The enumeration of returned fields implicitly confirms no filtering arguments are required.

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 verb+resource and then enumerates exactly which series (FEDFUNDS, SOFR, DGS2/5/10/30) and derived values (2s10s, 3m10y, EFFR vs IORB spread, curve shape signal) come back. This clearly distinguishes it from siblings like get_yield_curve, get_policy_spread, and get_series, which return only pieces of the same picture.

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?

"Use this instead of multiple individual calls when you need the full rate picture" gives an explicit selection rule against the alternative pattern. It falls short of a 5 because the alternative is described generically ("multiple individual calls") rather than naming the concrete siblings it replaces, and no when-not condition (e.g. single-series needs) is stated.

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