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

Annotations already declare readOnlyHint=true, idempotentHint=true and openWorldHint=false, so the safety profile is covered. The description adds non-annotation context the agent cannot otherwise know: that the tool is 'Free (nothing on this server is billed)'. It does not describe result size or ordering, but with annotations carrying the safety burden this is solid added 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?

A single dense sentence, front-loaded with the scope, followed by the entity types and the usage trigger. Every clause carries information; nothing is redundant padding.

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 has to describe the return contents itself — and it does, naming the two categories and the example-question field. Combined with the free/not-billed note and the coverage-check guidance, an agent has everything needed to call it correctly for a zero-parameter catalog 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?

The tool takes zero parameters, so the baseline is 4. The description correctly implies a call with no arguments and spends its words on what the list contains instead of inventing parameter semantics.

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 ('List') and a precisely bounded resource ('everything this server covers'), then enumerates the two entity types the list contains (money_fact keys with example questions, scheme_lookup countries). This directly distinguishes it from the sibling tools money_fact and scheme_lookup, which fetch the underlying data rather than the catalog.

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?

Gives an explicit trigger for calling it: 'call first if unsure whether a fact is covered' — a clear pre-flight/discovery condition relative to money_fact and scheme_lookup. It does not state any when-not-to-use case (e.g., skip it if you already know the key), so it stops just short of full routing guidance.

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