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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so safety is covered. The description adds genuinely useful behavioral detail beyond that: the cloud-init user-data is never returned, and it names the underlying endpoint GET /instance/{id}, which helps the agent understand scope and side-effect-free retrieval.

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 compact sentences, front-loaded with the returned field set followed by the negative disclosure and the endpoint. Every clause carries information and nothing is redundant.

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 burden of describing return contents, and it does so by enumerating state, type, template, disk size, networks, security groups, elastic IPs and snapshots, plus the explicit exclusion of user-data. Only minor gaps remain (e.g., error/not-found behavior), which are non-critical for a read tool.

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%, so both the id (UUID) and zone (with default 'zone chosen at login') are fully documented in the schema. The description adds only the {id} path fragment, which does not extend the schema's meaning; baseline 3 is appropriate.

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?

The description states a specific verb (retrieves details) and a single, well-defined resource (one compute instance), then enumerates the fields returned. 'One compute instance' cleanly distinguishes it from exoscale_list_instances and other get_* siblings without ambiguity.

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?

Usage is only implied: the singular 'one compute instance' plus the required id parameter signal that this fetches a single known instance. There is no explicit statement of when to prefer this over list_instances or when it should not be used, so the agent must infer the routing.

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