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

With annotations already covering read-only, destructive, and idempotent traits, the description adds useful behavioral context: it returns the DNS records the owner must add, and the domain only serves after records resolve and verification completes. It also details workspace alias resolution behavior. There is no contradiction with the annotations.

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 user-facing trigger and is dense with relevant behavioral detail. The workspace alias examples are useful rather than filler, and the closing statement about DNS records and verification earns its place.

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 multi-mode tool with no output schema, the description covers return value (DNS records to add), activation condition (records resolve and are verified), and the workspace alias details. It does not specify the exact shape of the DNS records or failure/error cases, but the schema plus description is largely 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?

Though schema coverage is 100%, the description adds meaning beyond the schema. It explains that site_id binds one specific Pro site, that target: 'workspace' makes the host a full alias of the workspace subdomain, and that site_id on target workspace names the root site at the bare path. This significantly clarifies the target and site_id parameters.

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 opens with an explicit use case ('Use when the user wants the site on their own domain') and clearly identifies the resource and action: pointing a custom domain at SnapHost. It also distinguishes the site-binding and workspace-alias modes, which separates it from sibling tools like remove_custom_domain, verify_custom_domain, and list_custom_domains.

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 states a clear triggering condition and explains the two target modes (site vs workspace), giving the agent enough context to select the tool. However, it never explicitly says when not to use it or points to alternatives like verify_custom_domain for checking status or remove_custom_domain for teardown, so exclusions are missing.

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