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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description adds useful cost context ('Free to call; does not consume account balance'), which goes beyond annotations. However, it doesn't describe pagination behavior for the limit parameter or how results are ordered.

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?

Two sentences, front-loaded with the core purpose and the specific values, followed by usage timing and cost note. Every clause earns its place with no filler.

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?

For a simple, read-only lookup tool with a fully documented schema, the description covers purpose, context, and cost. Minor gaps like return ordering or the absence of an output schema note are acceptable given the tool's simplicity.

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% with clear descriptions for both limit (defaults to 200, max 500) and search (case-insensitive name filter). The description adds no parameter-specific detail beyond the schema, so the baseline of 3 is correct.

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 states a specific verb and resource ('List available supported countries') and even enumerates the known values (Finland, Sweden, Estonia) with their purpose (IDs for countryId filters). This distinguishes it from lookup siblings like list_industries or list_job_functions.

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?

It clearly states when to use it ('when building geography-based segments before calling segment/count tools'), naming the downstream tools. It doesn't give explicit exclusions, but the 'before segment/count tools' framing establishes the workflow context well.

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