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

No annotations are provided, so the description must carry behavioral context; it does disclose the access tier (Pro/Enterprise) and the returned components (day's range, source count, confidence class, dollar-leg cross rate, corridor premium), including the sign convention for the premium. It does not mention rate limits, error behavior, or explicitly state read-only status, but for a read-style market-data query it supplies substantial context.

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 a single dense sentence with no filler; the core rate definition is front-loaded before the supporting return fields. The parenthetical and multi-clause construction reduce scanability slightly, so 4 rather than 5.

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?

Given a three-parameter tool with 100% schema coverage and an output schema, the description supplies the key invocation semantics: currency direction, data source type, returned metrics, premium interpretation, and key tier. It lacks alternative-tool routing, but the structured fields cover the rest adequately.

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 schema already documents a, b, and lang. The description adds economic meaning and direction beyond the schema by defining the quote as 'units of b per 1 a' and tying a/b to two emerging-market countries; it does not add lang semantics, but that is already in the schema.

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 the specific resource—the rate between two emerging-market currencies from public exchange listings—and the exact orientation (units of b per 1 a), plus the derived cross rate and corridor premium. That is more specific than the title, though it does not explicitly contrast the tool with siblings such as get_rate_stack or get_street_rate, so it lands at 4 rather than 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?

It gives no when-to-use or when-not-to-use guidance and names no alternatives among the many sibling rate tools. The only usage-adjacent sentence is an access constraint ('Pro and Enterprise keys'), not selection guidance.

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