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

Annotations already establish readOnlyHint, idempotentHint, destructiveHint=false, and a closed-world scope, so the safety profile is covered. The description adds genuinely new behavioral context beyond that: invoices are emailed automatically and 'there is no on-demand resend' — a real limitation on what the agent can promise the user, which the annotations do not convey.

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 core purpose and the returned fields before the scope clarification and the invoice caveat. Every sentence earns its place; no filler.

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?

There is no output schema, so the description carries the burden of describing return values — and it enumerates them concretely (current plan, monthly amount, last and next payment, recent invoices, trial state with days remaining). Combined with the read-only annotations, an agent has everything needed to call it 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 parameter semantics carry no risk and the baseline is 4. The description adding no param detail is appropriate here since there is nothing to document.

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?

Names a specific verb and resource ('Get the authenticated user's own subscription/contract status') and itemizes exactly what it returns: plan, monthly amount, payments, invoices, and trial state. The scoping clause 'Scoped to the signed-in user only' separates it from broader/multi-user tools, so an agent can distinguish it from the many other get_* siblings without opening a 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?

Usage is implied by the subject matter (use it to check the caller's own subscription/billing state), but there is no explicit when-to-use guidance, no exclusions, and no comparison to the closest alternatives such as get_pricing or get_account_info. An agent must infer the boundary between this and pricing/account tools.

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