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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds value beyond them: the auth requirement (company API key 'aa_...' or MCP OAuth access token), the fact that the bootstrap key is exempt from the active-plan requirement, and an explicit non-effect ('It does not change billing or charge a card'). It also enumerates the returned fields.

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?

Six short sentences, each load-bearing: purpose first, then when-to-use, then prerequisites, then auth, then return fields, then the negative scope. No filler or repetition of the tool name.

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 input parameters and no output schema, the description compensates by listing the return payload (planId, planStatus, periodYm, included, used, remaining, hardCap) and by covering auth, prerequisites, and non-effects. An agent has everything needed to decide and invoke correctly.

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 zero parameters, so the baseline is 4; there is no parameter semantics for the description to enrich. The description correctly does not invent any inputs.

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 precise verb and resource ('Read remaining quotas and plan entitlement for the authenticated company'), and the 'authenticated company' scoping separates it from tenant-level siblings. The following routing sentences make it unmistakable against billing_checkout, billing_machine_pay, and billing_portal.

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 an explicit trigger ('Call this when you need to know whether an active plan is in effect before registering OIDC clients or creating login links') and names three alternatives with the condition that selects each ('To start a human Pro checkout, use billing_checkout', 'billing_machine_pay only returns prepaid REST instructions', 'To manage an existing Stripe subscription, use billing_portal').

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