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

Annotations already declare readOnly/idempotent/non-destructive, so the description is free to add domain semantics — that the series is mid-market, pre-fee, and historical rather than predictive. It does not describe the shape of the returned series, which matters somewhat since there is no output 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?

Three tight sentences: what it shows and its scope first, then the caveats, then the trigger. Every sentence earns its place with no filler.

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 two-parameter read tool with full annotation coverage, the definition is essentially complete on inputs, semantics, and safety. The one remaining gap is that with no output schema, the description never says what the returned history looks like (series of points, granularity), leaving the return value underspecified.

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?

With 0% schema description coverage, the description carries the burden and largely does: 'from US dollars to another currency' fixes the base currency as USD so 'currency' is clearly the target, and the range list spells out the enum values in human terms. It does not state the expected format for the currency code beyond what the 3-letter regex implies.

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?

States a specific verb and resource ('Shows how the mid-market exchange rate ... has moved') plus the exact scope (24h/7d/30d/90d/1y). The clarifying line that mid-market is not the rate a payment is priced at separates it from the quote-pricing siblings without naming them.

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 it when someone asks how a currency has moved against the dollar' gives a concrete trigger, and 'it is not the rate a payment is priced at' plus 'a past series is no forecast' rules out two misuse cases. It stops short of naming the alternative tools (get_send_quote/get_receive_quote) for pricing questions, so routing is implied rather than explicit.

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