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

Annotations already declare readOnlyHint=false, openWorldHint=true and destructiveHint=false, but the description adds real value beyond them: it discloses the default destination (the account's sign-in email), the alternative destinations (another email or an https webhook POST), and the read-scope requirement. It does not cover idempotency of repeat requests or behaviour on an unknown id.

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?

Three short sentences, front-loaded with purpose, then destination rules, then the consent and scope caveats. 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 four-parameter subscription tool with full schema coverage and an output schema handling return values, the description supplies the missing operational context: default destination, redirect options, human-approval requirement and auth scope.

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%, so the baseline is 3, and the description earns above that by explaining the routing semantics of email and webhookUrl relative to the implicit default (the sign-in email) rather than merely restating the field names.

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 action (subscribe to a ship notification) against a specific resource (a planned capability), phrased so it is unmistakably distinct from capabilities_list, which only enumerates them. An agent knows exactly what this tool accomplishes without opening the 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?

"Ask the human first" and "Needs the read scope" give a clear consent and prerequisite condition, and "planned capability" implies the item is not yet shipped. It stops short of naming the alternative workflow (e.g. call capabilities_list first to obtain the id) or stating when not to use it.

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