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

With no annotations, the description carries the full burden and does so well: it declares read-only, states credentials stay with the caller and are never transmitted, notes matching is deterministic with no scores, and enumerates failure outcomes including under-published services. It does not mention rate limits, caching, or what an unknown/unregistered domain yields, so it falls short of a 5.

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 outcome list leads the sentence and the return shape, determinism, and safety guarantees follow in a compact block with no filler. It is dense and slightly overloaded for one sentence, but every clause carries information.

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?

With no output schema and no annotations, the description must cover both return shape and safety, and it does list the plan contents (protocol, endpoint, transport, version, published auth metadata) plus the read-only/no-credential posture. It leaves open edge behavior such as unknown registrable domains, so it is strong but not fully complete.

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 100% across both parameters, including the nested supports/auth/versions/transports and the clientAssumed default behavior, so the schema already does the heavy lifting. The description reinforces the role of client capabilities but adds no syntax or format detail beyond the schema, matching the baseline 3.

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 gives a precise verb+resource ('return HOW the client can connect' for a given domain) and enumerates the exact outcome space (ready | credentials-required | incomplete | broken | no-compatible-method), which makes its scope unmistakable. It never names discover_domain or check_readiness, so the agent gets no explicit sibling routing, keeping this at a 4 rather than a 5.

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?

The preconditions are stated ('Given a domain AND the calling client's capabilities') and the purpose implies when it is useful, but there is no explicit when-to-use versus discover_domain or check_readiness, and no exclusion conditions. Usage is implied rather than directed.

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