link_domain

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

Annotations only say it is a non-readonly, non-idempotent, non-destructive mutation; the description adds real value beyond that by disclosing the outbound fetch of an external URL, the one-domain-to-one-key invariant, and the enumerated failure causes (missing/non-JSON file, mismatched pubkey, domain already linked). It stops short of stating retry semantics or whether a failed verification leaves any partial state, which is why it is not 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?

Purpose is front-loaded in the first clause, then prerequisites, then failure modes, then alternative. Dense but tight; the JSON snippet and parenthetical example earn their space, though the error enumeration is slightly verbose relative to the single-parameter tool.

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 verification tool with one parameter, no enums, and an output schema already covering the return value, the description supplies everything else an agent needs: the setup step, credential source (whoami), format constraint, uniqueness invariant, and error recovery path.

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 coverage is 100% and the schema already says 'host name you control, e.g. agent.example.com'; the description's 'plain host' note and identical example largely restate that. Baseline 3 applies since the schema carries the parameter documentation.

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?

States a specific verb and resource ('prove you operate a domain'), names the mechanism (NIP-05 file fetch), and explicitly contrasts with the sibling link_wallet. An agent can distinguish it from link_wallet and issue_receipt without opening any schema.

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?

Gives a concrete ordered precondition (publish the .well-known/nostr.json file with the exact JSON shape, get the pubkey from whoami), then the call, plus an explicit alternative redirection to link_wallet for the payment wallet. When-to-use, prerequisites, and the sibling boundary are all covered.

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