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

Annotations already cover readOnly/idempotent/destructive, yet the description adds substantial context: the semantics of `capped: true` (lower-bound figures during rollup backfill), the fact that `lifetimeMeteredEstimateUsd` is a diagnostic and not an amount owed, and that `pendingUsd` matches the Dash's PENDING. This is exactly the interpretive guidance an agent needs for a metrics tool.

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?

Dense and front-loaded, with the core framing in the first clause and the sibling alternative named mid-paragraph. It is long, but nearly every clause disambiguates a field or a caveat; only the dual money-figure explanation is slightly verbose.

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 explaining return values — and it does: reads, writes, ratio, rate card, both money figures with interpretations, and the `capped` flag. An agent can act on the result without further documentation.

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 parameter semantics are trivially satisfied (baseline 4). The description instead spends its effort documenting return fields, which is appropriate given the empty schema.

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?

Opens with a specific framing ('Usage METER for the org — activity volume, not a bill') that names the verb, resource, and the key distinction from billing. An agent immediately knows this reports metered activity rather than invoiced money.

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?

Explicitly routes the agent: 'For the full picture — subscription, charges and on-chain payments across every link — use `billing_summary`.' It also states a non-obvious usage fact (reading the meter is not charged), which removes hesitation about calling it.

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