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

The description adds substantial context beyond the annotations: paid-plan prerequisite, exact DNS records returned, the need to relay them to the user, verification gating, automatic HTTPS on first visit, and the fact that the share URL continues to work. These are operational details an agent needs but cannot infer from readOnlyHint=false, openWorldHint=true, idempotentHint=false, and destructiveHint=false.

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?

The description is front-loaded with the action and prerequisite, then moves through the DNS output, verification step, HTTPS behavior, and share URL continuity. Every sentence contributes necessary operational guidance without repetition.

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?

Although an output schema exists, the description still explains the key return values (ownership TXT and routing CNAME/A records) and the verification lifecycle. Combined with the paid-plan caveat, verbatim relay instruction, HTTPS behavior, and share URL continuity, it is complete for this mutation 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?

The schema fully documents both required parameters, including the domain format and project_id meaning. The description reinforces the domain example and ownership requirement but does not add meaningful parameter semantics beyond what the schema already provides.

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 and resource: attach a user-owned domain to a spawnpoint project. It gives a concrete example and distinguishes the operation from verification and removal by naming the next lifecycle step.

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?

It explicitly says this requires a paid plan, that DNS records must be relayed verbatim, and that verify_custom_domain should be called once those records exist. This gives clear when-to-use and next-step guidance rather than leaving the workflow implicit.

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