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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds the useful non-obvious facts that data is 'credential-free public Numbeo data' from numbeo.com, telling the agent no auth is needed and where it comes from. It stops short of noting freshness/caching or data vintage.

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 short sentences, front-loaded with the output scope, then provenance, then the sibling routing. Nothing redundant; each sentence carries distinct information.

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 an output schema present, the description needn't explain return shape, and it still concisely characterizes what comes back (country itemized prices plus per-city indices). For a one-parameter read-only lookup, nothing an agent needs to call it correctly 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 100% and the single country parameter is documented there (including the spelling convention 'e.g. Vietnam'). The description adds nothing about parameter syntax, so the baseline of 3 applies – the schema does all the work.

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 (returns) and resource (aggregate cost-of-living prices for a country) and explicitly distinguishes itself from the country-vs-city sibling by naming numbeo_cost_of_living_city. An agent can tell what this returns and how it differs from the city variant without opening a 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?

It routes the agent explicitly: 'Use numbeo_cost_of_living_city to get a Numbeo city's cost-of-living prices,' giving a clear condition for choosing the alternative. It does not address the numbeo_cost_of_living_rankings or numbeo_indices_* siblings, so coverage of alternatives is only partial.

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