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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint=false, so safety and repeatability are fully covered. The description adds only the useful detail that verification status is part of the result; it says nothing about ordering, pagination, or behavior for projects with no domains, which is a modest but acceptable gap given the annotation coverage.

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?

One sentence with the operation, scope, and return content front-loaded, and no filler or repetition of the title.

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 simple, read-only single-parameter list tool with no output schema, the description conveys both the scope and the shape of what comes back (domains plus a verified flag). Output structure and edge cases are left implicit, but nothing critical to invoking it correctly is missing.

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 single parameter is fully documented in the schema (100% coverage) with its pattern and meaning, so the schema carries the load. The description adds the scoping nuance that the project id selects whose domains are listed, which is minor but consistent with the 3 baseline for high-coverage schemas.

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 names a specific verb and resource ('List ... custom domains') and adds the returned attribute ('whether each is verified'), which cleanly separates it from add_domain, remove_domain, and verify_domain in the sibling set. It stops short of naming those siblings explicitly, so it is clear but not fully differentiated.

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: it lists a scoped set of domains for a project, so an agent can infer it is the read path for the domain lifecycle. There is no explicit when-to-use statement and no mention of alternatives such as get_public_paths or verify_domain when the verification flag comes back false.

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