list_countries

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

Annotations already declare readOnly/destructive=false, so the description adds meaningful extras: the complete one-shot listing (no pagination), the exact row count (250), and that the data is cached reference data. This rises above the annotation baseline.

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?

Dense but not bloated: it packs the row count, field list, usage condition, and error behavior into a single tight sentence. A minor over-elaboration on the exact reject message is acceptable, so a 4, not a 5.

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?

Covers the data set size, field schema, usage trigger, and failure mode. An agent can decide and call this tool correctly without opening the schema or consulting anywhere else.

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 parametersthority, so the schema fully covers it. The description adds no parameter explanations because none are needed — a baseline 3 is appropriate; there is simply nothing further to clarify.

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 and resource (

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?

Explicitly says when to use it: tie to party addresses, and notes the exact spelling requirement (anything else → 422). It also names an alternative class (add_party_address) where this dictionary is the prerequisite.

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