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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint=false), so the description's main added value is the estimate-versus-commitment distinction: "the final terms are shown in the Poplin app before anything is confirmed." That is genuinely useful behavioral context an agent needs before quoting numbers to a user. It does not mention pricing assumptions beyond 'standard pricing' being fixed, or any auth/rate-limit behavior.

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 with the capability stated first, the usage trigger second, and the caveat last — a sensible front-loaded order. The enumeration of rate/fees/limits/speed is informative rather than padding, though the opening sentence is dense enough that it could be split for scanability.

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 usefully enumerates what comes back (sent amount, received amount, rate, fees, limits, speed), which is exactly what an agent needs to know before calling. The remaining gap is the currency/amount direction ambiguity noted above; otherwise nothing essential for a read-only estimation tool is missing.

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 0%, so the description carries the full burden, and it only partially compensates. The phrasing "how much is sent in US dollars, how much arrives in the other currency" gives conceptual meaning to the amount_is enum (sent vs received), but it never clarifies ISO format expectations for currency/country or, critically, whether `currency` is the source or destination currency. Field names alone still leave the source-currency assumption ambiguous.

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 (estimates) and a precisely scoped resource: paying a bank account from a Poplin account, broken down into amount sent, amount received, rate, fees, limits and speed. The send direction and 'personal and business accounts at standard pricing' scope make it separable from siblings such as get_receive_quote and get_stablecoin_transfer_quote without opening any schema.

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 what a payment would cost or how much the recipient would get" gives an explicit trigger condition, and the closing sentence clarifies that this is pre-confirmation estimation only. It stops short of naming the alternative tools (e.g. get_receive_quote for inbound) or stating when not to use it, so it is clear context without full routing guidance.

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