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

Annotations already establish readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds genuinely new context: the tool works without an API key, and the actual signup/payment happens in the user's browser rather than server-side, which explains why a 'buy' tool is read-only. No return shape is described, but for a URL-producing tool that is a minor omission.

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?

Two sentences, front-loaded with what the tool produces, followed by the usage trigger. Every clause earns its place — no filler, no repetition of the title or schema.

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 2-parameter, read-only tool with no output schema, the description covers what it returns (a URL), its availability, and the user flow. The one missing piece an agent would want is the relationship to buy_domain, so it falls just short of 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% — both 'domain' (with an example) and the optional 'priceUsd' are fully documented in the schema, including the fallback behavior when price is omitted. The description adds no parameter-level detail beyond the schema, so the baseline 3 is correct.

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 concrete verb+resource: 'Build a one-click purchase URL ... to buy a domain on namemy.app'. An agent knows exactly what it gets back (a URL). However, it never names or distinguishes itself from the sibling buy_domain, so the boundary between 'get a link' and 'actually buy' is left implicit.

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 clear trigger condition: 'Use this when the user has decided on a name they like'. This is real usage context, not just a restatement. It stops short of an exclusion clause — it does not tell the agent when to prefer buy_domain over this tool, which is the most likely confusion given the sibling names.

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