Account Usage

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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the safety profile is covered. The description adds real behavioral context beyond that: the exact return payload (including renewal date) and the 'CREDIT COST: 0' note, which tells the agent the call is free and safe to make speculatively. It omits any note on staleness/caching of usage figures.

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 plus a cost line; the trigger phrases are front-loaded and the return enumeration is dense but readable. Slightly lead with routing rather than the core purpose, but nothing is wasted.

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's field enumeration is necessary and present, and annotations cover safety. Minor gap: it advertises 'how do I upgrade or top up' as a trigger, yet the tool only reports subscription status, which could set a slightly wrong expectation about whether an upgrade action occurs.

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?

Single optional parameter with 100% schema description coverage ('YYYY-MM; default current month'), so the schema carries the semantics. The description only implies a current-month default and adds no format or range guidance beyond the schema, making 3 the correct baseline.

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?

Specific verb+resource: it enumerates exactly what is returned (plan tier, billing period, credits used/included/remaining, API calls, subscription status, renewal date). That enumeration clearly separates it from auth_status and the dev_* tools without needing to open the 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 explicit trigger utterances ('how many credits do I have left', 'what's my usage this month', 'what plan am I on'), which is strong when-to-use guidance. It does not name an alternative or state a when-not-to-use case, so it stops short of a 5.

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