Get exchange rate fluctuation

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

With no annotations provided, the description carries the burden well: it discloses the returned fields, the sign convention with a worked interpretation (positive = symbol strengthened), and the plan gating. It does not mention rate limits or behavior when dates are invalid/reversed, which keeps it below a 5.

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 output fields are front-loaded in the first clause, followed by the sign convention and plan note. The sign-convention sentence is long but each part earns its place by preventing a real interpretation error; 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?

There is no output schema and no annotations, so the description must specify the response shape and safety/permission context — it does both by enumerating return fields and stating the plan requirement. Minor gap: no guidance on default date behavior beyond what the schema provides or on large-symbol responses.

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 base, startDate, endDate, and symbols are already fully documented in the schema, including defaults and the symbols guidance. The description adds no parameter-level meaning beyond the sign convention, so the baseline 3 is appropriate.

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 ('Returns how currencies moved between two dates') and enumerates the returned metrics (start rate, end rate, absolute change, percent change). It is clearly distinct from a raw rate lookup, though it does not explicitly name the closest siblings (get_time_series, get_historical_rates) that an agent might confuse it with.

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?

It gives a clear operational precondition ('Professional plan and above') and implies usage for two-date comparison, but it never says when to prefer this over get_time_series or get_historical_rates. The choice among siblings is left to inference.

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