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

Annotations only declare readOnlyHint and openWorldHint, but the description adds real behavioral context: unknown codes error out, only live countries answer, TN/MA require an API key, and specific failure codes (country_not_available, key_required) are named. That is material information an agent cannot get from the annotations.

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?

Front-loaded with the core action and code format, then branches by country. It is somewhat long and repeats per-country code examples already present in the schema, but with no output schema the field enumerations earn their space.

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 carries the return-value burden and does so per country (names, capital, region, population, CNRC/CASNOS offices; ISO 3166-2, INS code, three-language names, chief town). Auth, error behavior and the code-discovery alternative are all covered.

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 schema already documents code, lang and country in detail including the same examples (16 for Alger, TN-11, MA-06). The description largely restates that per-country code semantics rather than adding new syntax or format meaning, so the baseline 3 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 specific verb and resource ('Get one Algerian wilaya by its two-digit code') and immediately scopes the tool across three countries with distinct semantics. It is clearly distinguishable from the sibling list_wilayas, which it names as the code-discovery route.

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 a clear entry condition (a two-digit code, obtained via list_wilayas), states the failure mode ('returns an error when the code is unknown'), and notes that TN/MA need an API key. It routes to a sibling but does not state an explicit when-not-to-use case beyond that.

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