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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds value beyond that by naming the underlying endpoint and sketching the return envelope '{ domains: [...] }', which is genuinely useful since no output schema exists. Pagination and error behavior remain unstated.

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 the purpose and followed by endpoint and return shape. The API path line is slightly redundant with the endpoint implied by purpose, but it earns its place by disambiguating scope.

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 single-parameter read tool with no output schema, the description is nearly complete: purpose, endpoint, and return shape are all present. It falls short only on pagination/ordering and what happens with an unknown app.

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 coverage is 100% and the single 'app' parameter is documented with name-or-id format, so the schema does the heavy lifting. The description reinforces that the path is app-scoped but adds no new semantics such as accepted formats or validation rules; 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 ('List an app's custom domains') plus what the results carry ('TLS/canonical status'), so an agent knows exactly what comes back. There is no sibling tool operating on domains, so explicit differentiation isn't needed, but it also doesn't anchor itself against the broader list_* family.

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 required 'app' parameter signals it is a per-app query, and the description says it lists an app's domains. There is no statement of when to prefer this over, say, scalingo_get_app or scalingo_request, and no exclusions or prerequisites.

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