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

Annotations only declare readOnlyHint and openWorldHint; the description adds real behavioral context beyond them: the methodology (covered interest parity from an independent mid and central bank policy rates), the fact that basic use is free while the quotedRate comparison is gated behind a paid key, and what the response conceptually contains (margin of error, annualized hedge cost/earn, margin). It does not discuss precision, rate staleness, or supported tenor limits beyond the schema.

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?

It is short and front-loads the core output, but the final clause ('the forward a bank quoted is held to it: how much is margin') is syntactically awkward and takes a second read to parse. No filler sentences, but the phrasing costs clarity.

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 five parameters, no output schema, and only minimal annotations, the description carries the burden well: it explains what is computed, the data sources, the free-vs-paid split, and what the quotedRate branch yields. What remains missing is minor — no indication of rounding, base-currency conventions beyond the schema, or error behavior for unsupported pairs.

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 coverage is 100%, so all five parameters are already documented in the input schema, including 'from', 'to', 'tenorDays', 'amount' and 'quotedRate'. The description only restates that quotedRate is a bank-quoted forward to be benchmarked, which mostly duplicates the schema's own wording, so the baseline 3 applies.

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 computation (estimated fair forward rate for a currency pair and tenor via covered interest parity) plus two auxiliary outputs: hedge cost per year and, when quotedRate is supplied, the bank's margin. It does not name any sibling tool to differentiate from, so it falls short of a 5.

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 implied through the tiering language ('Free' vs 'With a paid key and quotedRate'), which tells the agent that the margin-comparison mode requires a paid credential and the quotedRate parameter. There is no explicit when-not guidance and no mention of alternatives such as get_corridor_rates or rate_deal_history that also deal with rates.

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