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

With no annotations, the description carries the full burden and does substantial work: it discloses that the tool is free, requires no payment/challenge, gives the HTTP equivalent URL, pins the data vintage (business days 1990-01-02 through 2026-10-09, collected Oct 2026 from the Treasury feed), states dates after 2026-10-09 are not covered, and pins reproducibility to a SHA-256 corpus. It stops short of describing the returned document's shape or whether the call is cached/side-effect-free.

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?

Purpose is front-loaded, but the opening sentence lists the returned fields twice ('the contract, criteria, data vintage and licence... : the endpoint contract, the 14 tenors, the source line, ...'), and 'no payment required: call directly without payment (no x402 challenge; this tool is free)' says the same thing three ways. The dense em-dash chaining makes it harder to scan than necessary.

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 zero-parameter, no-output-schema metadata endpoint, the description covers provenance, coverage window, licensing and reproducibility, which is what an agent needs to decide to call it. The one real gap is that the exact contents/shape of the returned document are only gestured at rather than enumerated precisely.

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. The schema is empty and there is nothing for the description to compensate for; no misleading parameter claims are made.

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 names a specific resource: the contract/tenancy/vintage/licence metadata document for the Treasury Curve History service, and enumerates the sections it contains ('the endpoint contract, the 14 tenors, the source line, the settled vintage text and the licence line'). It does not name its obvious siblings (rates_curve, rates_history, rates_spreads) to distinguish itself, but the 'schema' role is unmistakable.

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?

'Read these before paying' gives an explicit ordering instruction relative to the paid rates endpoints, and 'call directly without payment (no x402 challenge; this tool is free)' clarifies that no payment flow is required. It never names the specific alternative tools or states any exclusion, so it falls short of a full when/when-not treatment.

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