get_rate_fluctuation

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

With no annotations provided, the description carries the full burden. It discloses the Business plan requirement and the 366-day range constraint, which add transparency. Still, it does not explicitly state read-only semantics, rate limits, or error behavior; the verb 'Get' only implies a safe operation, so coverage is moderate.

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 description is two short sentences with no filler. The core action and output details are front-loaded, and the plan requirement is isolated as a separate, clear sentence. Every sentence contributes value, making it optimally concise.

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?

Despite having no output schema and no annotations, the description explains the return values (start rate, end rate, absolute and percent change per currency) and the critical constraints (date format, max range, plan level). It does not detail response structure or error handling, but the tool's simplicity and the schema's completeness make the description sufficient for an agent to invoke it correctly.

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 goes beyond the schema by adding the crucial constraint that the date range must be at most 366 days, and it confirms the YYYY-MM-DD format, which is already in the schema. This enrichment of the start_date/end_date semantics justifies a 4.

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 identifies a specific action ('Get how exchange rates moved') on a clear resource (exchange rates) and enumerates the exact output fields (start rate, end rate, absolute change, percent change). It differentiates from sibling tools by scoping to 'between two dates' and imposing a 366-day limit, but it does not explicitly name alternatives, so it falls just 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?

The description gives useful context (date range, maximum span) and a plan requirement, which imply when the tool is appropriate. However, it does not explicitly mention when to use this tool versus get_historical_rates, get_timeseries_rates, or get_latest_rates, nor any exclusions. Guidance is implicit rather than explicit.

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