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

Annotations already establish readOnlyHint=true and destructiveHint=false, and the description adds genuinely new context: the required key scope (billing:read or billing:write) and an explicit data-boundary disclosure that the address is never returned. The action_url explanation also clarifies a non-obvious field.

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 sentences, front-loaded with the resource and scope, then the field list, then the alternative. Parentheticals are short and each sentence carries information that is not repeated elsewhere.

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 present, the description assumes responsibility for describing returns and does so by enumerating status, version, currency, country, vat_status, and action_url. Auth scope and the companion write tool are also covered, leaving no material gap for a zero-parameter read.

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 schema baseline is 4 and there is nothing for the description to compensate for. The description correctly does not invent parameter guidance.

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 opens with a specific verb and resource ('Read this account's billing profile') and then enumerates the exact fields returned, so an agent knows precisely what comes back. It also names the mutating counterpart, plan_profile_update, which distinguishes it from siblings like get_profile and plan_status.

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 states the use case (reading the billing profile), names the alternative tool and the condition selecting it ('To change it, use plan_profile_update with the version read here'), and warns that the address is out of scope. An agent needs no further inference to choose correctly.

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