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

Annotations already flag readOnly/openWorld, and the description adds genuinely new behavioral detail: rate orientation semantics, automatic flipping with a note when the rate is given the other way round, and the degraded behavior when quotes is empty. This is exactly the kind of context annotations cannot carry.

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 sentences, front-loaded with the core operation and the input contract before the fallback behavior. Dense but every clause carries information; minor verbosity in the enumeration of outputs.

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?

With no output schema, the description compensates by listing the return values and the no-quotes fallback. It leaves minor gaps such as error behavior for invalid currency codes or how ranking ties are broken, but an agent has enough to call 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 coverage is 100%, so baseline is 3, but the description adds meaning beyond the schema by explaining that rates are receiving-per-one-sending and that reversed rates are flipped and noted, plus clarifying that the agent is responsible for sourcing provider quotes. It does not explain receive_country's role beyond the schema's own text.

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 ('Exact math on sending money abroad or changing currency') and enumerates the concrete outputs: what arrives per provider, ECB markup, total cost percent, ranking, and World Bank benchmark. Clearly distinct from siblings like compare_prices, which is about product prices rather than FX transfers.

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?

Tells the agent what it must supply ('you find the quotes') and describes the no-quotes path ('returns the reference rate and the benchmark'), which effectively communicates two usage modes. It does not explicitly name an alternative tool or state exclusions, so it stops short of a 5.

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