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

Annotations already declare destructiveHint=true and idempotentHint=false, so the risk profile is known. The description adds genuinely useful value with 'Can affect live routing', a concrete impact warning not captured by annotations. However, it omits whether DNS/verification is required, whether the domain must already be owned, and what happens on the live service during propagation.

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, front-loaded with the action and immediately followed by the impact warning. Nothing is wasted, though the extreme brevity is under-specification rather than true tightness.

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 12-parameter mutation tool with no output schema and 0% schema description coverage, the description is far too thin. An agent gets no guidance on required versus optional fields, port targeting, or domain verification, all of which materially affect a successful call to a destructive, non-idempotent operation.

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 0% across 12 parameters, and the description names no parameters at all. The four required identifiers (projectId, environmentId, serviceId, domain), targetPort, and the non-obvious approval_id/beon_* fields are left entirely unexplained, so the description does nothing to compensate for the coverage gap.

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 ('Attach') and resource ('custom domain') with the scope ('to a service environment'), which is clear and distinguishable from write siblings like railway_create_service_domain. It stops short of explicitly contrasting with that near-identical sibling, so no sibling differentiation credit beyond the resource wording.

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 when-to-use, prerequisites, or alternative guidance is given. With siblings such as railway_create_service_domain and railway_delete_custom_domain in the same namespace, the description never says which one applies or when this should be chosen over them.

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