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

Annotations already establish that this is a read-only, idempotent, closed-world operation. The description adds substantial beyond-annotation context: owner authority is required for the billing block, unauthorized callers get only the usage meter with a `note`, Xenarch degradation is surfaced as `payments: null` plus `paymentsError`, historical payment links are fanned out, and reading billing is not charged.

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?

The core value is front-loaded in the opening phrase, and the dense sentence structure packs in useful return-shape and failure-mode details. It is long and somewhat paragraph-heavy, but almost every clause carries operational meaning.

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 and zero input parameters, the description carries the burden of explaining what comes back. It does so thoroughly, covering the full billing block, the degraded Xenarch path, the non-owner partial result, and the absence of billing charges for the 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 zero parameters, so there is no parameter semantics to explain. A baseline of 4 is appropriate because the description does not need to compensate for any schema gaps.

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 names a specific resource — the org's whole billing picture — and enumerates the returned components: subscription, caps, money states, charge ledger, confirmed on-chain payments, and usage meter. This is far beyond restating the title and lets an agent recognize the tool's scope immediately.

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 clearly states the authority prerequisite for the full billing block and explains what non-owner callers receive instead. However, it does not explicitly compare this tool to the sibling `usage_summary`, nor does it say when to choose the narrower usage-only tool versus this full billing view.

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