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

Beyond the supplied readOnlyHint and idempotentHint annotations, the description discloses operational constraints: 3 slots per workspace on premium, root-domain-plus-www counting as one slot, and the rule that free accounts cannot bind new domains while existing ones keep working. It also describes the return structure (progress, certificate expiry, paths, slot usage), which is valuable since there is no output schema.

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 purpose and return fields are front-loaded, and every clause contributes useful detail about slot counting or premium restrictions. The first sentence is dense with parentheticals, but no sentence is redundant.

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 zero-parameter, read-only listing tool with no output schema, the description supplies the missing return-value context (progress fields, certificate expiry, path mappings, slot usage) and the key business rules (premium slots, free-account binding restriction). An agent has enough information to invoke and interpret this tool correctly.

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 tool takes no parameters, so the baseline is 4. The description correctly spends no space on parameter semantics and instead focuses on what the tool returns and when to call it.

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 ('List the custom domains bound to this workspace') and enumerates the returned fields: progress state, certificate expiry, path mappings, and slot usage. This clearly distinguishes it from sibling domain tools such as bind_domain, unbind_domain, or verify_domain.

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 names two triggers: 'when the user asks which domains they have' and 'when you need a domain_id'. It does not explicitly exclude mutation-oriented siblings like bind_domain or set_domain_route, but the read-only framing and trigger conditions provide clear context.

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