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

readOnlyHint=true already tells the agent this is a safe, non-mutating read. The description usefully adds the shape of the returned records (id, description, visibility) and the backing endpoint (GET /1.3/zone), which matters since there is no output schema. It does not mention pagination, result ordering, or auth requirements, so it adds value without being rich.

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 short sentences plus an endpoint reference, front-loaded with the resource and its returned fields. Every clause earns its place and nothing needs to be scrolled past to reach the essential 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 no input parameters and no output schema, the description carries the burden of telling the agent what comes back, and it does so adequately by naming the three returned attributes. Minor gaps remain around whether the list is paginated or sorted, but for a simple global lookup this is close to sufficient.

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 no parameters, so the baseline is 4. The id-format examples (fi-hel1, de-fra1, us-chi1) describe return values rather than inputs, so they don't add parameter semantics, but there is nothing to under-document.

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 (list) plus the resource (zones/data centres) and enumerates the returned fields (id, description, public/private cloud) with concrete id examples. It's the only zone-related tool among the siblings, and the note that zone ids are consumed by every other resource makes its distinct role unmistakable.

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?

"Zone ids are used by every other resource" gives clear context for why and when an agent would call this first, e.g. to resolve a zone id before creating servers or storages. It stops short of explicit when-not guidance or naming alternatives, but for a zero-parameter enumeration tool the usage context is well signalled.

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