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

Annotations only declare readOnlyHint=true; the description adds real interpretive context beyond that: under 'sponsored' the business is not metered so limit/left/out are not a real cap, under 'trial' there is no paid plan yet, and 'legacy'/'plan-label' change how the allowance should be read. It does not discuss freshness/latency or auth, but the disclosed caveats meaningfully shape how the returned numbers must be interpreted.

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?

Front-loaded with the subject ('this billing period's action usage') and densely information-bearing, with no filler sentences. The structure is a near-run-on enumeration of fields and flags that is hard to scan, costing it a point despite the absence of waste.

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, the description correctly carries the return-value burden and explains each notable field and its caveats, so an agent can interpret the response without external docs. It could be slightly more complete on cadence (e.g. whether values are real-time vs. end-of-day), but for a parameterless read tool it is largely self-sufficient.

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 nothing parameter-side for the schema to cover. The description instead spends its budget on return-field semantics, which is the right use here, though that belongs to contextual completeness rather than parameter documentation.

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+resource ('this billing period's action usage') and enumerates exactly what the payload contains (used vs allowance, reset time, prepaid balance, spend/out status, usage by kind, hours saved). It also names the sibling get_subscription as the route for Stripe billing line items, so an agent can distinguish the two 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?

Gives one explicit routing rule ('for the plan's Stripe billing line items use get_subscription'), which is genuine when-not guidance. It does not, however, frame the broader context of when an agent should reach for this tool versus other account-level tools like get_business_overview or get_financial_summary.

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