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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so safety is covered. The description adds genuinely non-obvious behavior: what an empty destinations list means, and the post-call obligation to display get_started_url. It does not mention return shape beyond the fields it names, but there is little more to disclose for a read-only lookup.

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?

Four sentences, front-loaded with the return description followed by usage, empty-case semantics, and the UI instruction—every sentence carries content. 'When paying someone else's bank account' and 'sending to other people's bank accounts' slightly restate the same scope, a minor redundancy.

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, so the description must carry return-value burden and does: it enumerates the returned fields (countries, currencies, payment rails, delivery time), names get_started_url, and explains the empty-list meaning. Combined with a single fully documented parameter and full annotation coverage, an agent has everything needed to call and interpret this tool.

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% and the single from_country parameter already documents the ISO 3166-1 alpha-2 format and the 'ask, do not assume' rule. The description restates the semantics of from_country ('a person living in from_country') but adds no format or validation detail beyond the schema, so the baseline 3 applies.

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 a precise verb (returns) and a precisely scoped resource: countries, currencies, payment rails and delivery times reachable from a given sender country. The scope constraint ('paying someone else's bank account') implicitly separates it from siblings get_exchange_rate and quote_send, which concern pricing rather than destination coverage.

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?

Explicit usage trigger: 'Use it to answer whether Morse can send from one country to another.' It also defines the empty-list case and instructs the agent to surface get_started_url. It stops short of naming the alternatives (get_exchange_rate, quote_send) and saying when not to use this tool, which a 5 would require.

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