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

Annotations already declare readOnly, idempotent, and closed-world, so the safety profile is covered. The description adds genuinely new information beyond those fields: that the call is free and that nothing on the server is billed, which is pricing context an agent cannot get from the annotations or schema. It also previews the response shape (keys with example questions, countries).

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?

A single sentence front-loads the scope and appends the routing directive; the parenthetical about cost is tucked in without breaking flow. No filler, no restatement of the title.

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 still conveys what comes back at a useful level of abstraction (fact keys plus example questions, country list). For a zero-param read-only discovery tool this is everything an agent needs before calling.

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?

Zero parameters with an empty required-free schema, so there is nothing for the description to disambiguate. Baseline for a no-param tool 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?

States a concrete verb (list) and two precise resources: every money_fact fact_key with an example question, and every scheme_lookup country. Naming money_fact and scheme_lookup directly ties it to the sibling tools, so an agent can tell this is the discovery/index tool rather than a lookup execution.

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?

"call first if unsure whether a fact is covered" gives an explicit conditional trigger, and the zero-arg free nature removes any cost barrier to over-calling. It stops short of naming the alternative path for when coverage is already known (call money_fact/scheme_lookup directly), so not a full when/when-not mapping.

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