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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is covered structurally. The description adds genuinely new behavioral context: results are scoped to live mode only (test-mode data excluded), values are aggregates rather than per-customer rows, MRR is denominated in minor units, and no account or Stripe identifiers are exposed. What it omits is whether the snapshot is point-in-time or windowed, and whether any filtering is possible.

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?

Two tight sentences, front-loaded with the return payload and followed by the privacy/scope constraint. No filler, no restatement of the title, and every clause carries information.

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?

An output schema exists, so the description is not obliged to explain return values, and the safety profile is covered by annotations. It covers scope, units, and privacy adequately for a zero-argument read tool; the only real gap is that the temporal basis of the MRR figure (current snapshot vs. period) is left implicit.

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 nothing for the description to disambiguate and the baseline is 4. The mention of 'minor units' and 'live-mode' describes output semantics rather than inputs, which is appropriate here.

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 specific verb-plus-resource (returns an aggregate MRR summary) and enumerates exactly what comes back: active live-mode subscription count, MRR in minor units, and plan mix. An agent knows precisely what this produces, though it never distinguishes itself from the similar-sounding sibling usage_summary.

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?

There is no when-to-use statement, no prerequisites, and no named alternative. The phrase 'active live-mode subscription' hints at scope, but nothing tells an agent whether to reach for this versus usage_summary or subscription_status when it needs billing metrics.

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