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

Annotations already cover the safety profile (readOnlyHint=true, openWorldHint=true, destructiveHint=false). The description adds genuine value beyond them: the underlying API path (GET /zone), the fact that the response carries API and object-storage endpoints, and the domain fact that resources are pinned to exactly one zone.

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 what is listed, then what the response contains, then the API route. Every sentence earns its place and nothing is padded.

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 zero-parameter, read-only list tool with no output schema, the description covers the essentials: what is returned (zones with their endpoints) and the domain constraint that resources belong to one zone. Minor gaps such as pagination or ordering are not disclosed, but they are unlikely to matter for a small, fixed zone list.

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 and there is nothing for the description to disambiguate. The schema is empty and fully covered; no parameter semantics are missing.

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?

Specific verb+resource ('List the Exoscale zones') with a parenthetical gloss clarifying what a zone is, plus the exact payload contents (API and object-storage endpoints). It is trivially distinguishable from every sibling, which operate on instances, volumes, DNS, etc.

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?

No explicit when-to-use or when-not statement, but usage is strongly implied by the sentence 'Compute, storage and network resources live in one zone each,' which tells the agent zones are the geographic anchor for resource placement. There is no alternative zone-listing tool to route away from, so the omission is minor.

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