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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. Beyond that the description adds real value: drift is expressed in bps and sent currency, above_negotiated is set only past the stored tolerance, missing figures are null, and the payment remains with the customer's own bank. It does not say how far back history goes, whether results are paginated, or whether prepared-only payments appear.

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?

The content is informative but delivered as one dense run-on block. 'Keyed.' at the start and 'A router key is required.' at the end state the same prerequisite twice, which is waste, and the return-field inventory would read better as a list.

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?

There is no output schema, so the description properly carries the return-shape burden by naming the compared figures, drift units, and the null convention. Combined with 100% schema coverage on inputs, the definition is nearly complete; the main omission is any statement about history depth or result volume.

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%, so the baseline is 3. The description adds only the framing that 'from' and 'to' define a corridor plus a customer, and restates that a router key is required for access_key; it gives no added syntax or constraints for any of the four parameters.

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 gives a specific verb and resource: 'Returns the dated history of comparisons for one customer and corridor', and it spells out the three things compared (payment rate, negotiated deal, public market price). That is enough to separate it from read-only siblings like get_corridor_rates or get_rate_receipt, though it never names those siblings 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?

There is no when-to-use / when-not-to-use guidance and no named alternative. The only conditional content is the prerequisite 'A router key is required.' An agent must infer from the phrase 'dated history of comparisons' that this is for retrospective auditing rather than live pricing.

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