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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, so the safety profile is covered; the description adds genuinely new context beyond that: the microcents unit scale with a worked conversion, that values are returned pre-formatted, and the intended pre-flight-check workflow. It omits anything about openWorldHint network behavior or failure modes, keeping it off a 5.

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?

Three tight sentences with zero filler; the default action and unit scale are front-loaded ahead of the workflow advice. Every sentence contributes distinct information (purpose, return semantics, unit, when to call).

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 carries the burden of explaining return values, and it does so well for action=balance (units, formatted values) but only vaguely for action=usage ("usage statistics"), leaving the agent guessing at that mode's shape. For a single-param read-only tool, though, nothing essential to invoking it correctly is missing.

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?

Schema coverage is 100% and the single enum parameter already documents both values, so the schema carries the load. The description does add meaning by explaining what each action returns rather than just naming it, which nudges this to the baseline rather than above it, since no format, default-confirmation, or edge-case semantics are added for the parameter itself.

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 and resource ("Read account credit data") and then enumerates the two modes it covers: current credit balance and usage statistics. An agent can distinguish this from cost-estimation or pricing siblings without opening the schema, since the description makes clear it reads actual account credit rather than estimating future spend.

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 concrete when-to-use guidance: "call it before an expensive crawl or batch to confirm there are enough credits." That covers the primary selection scenario, though it never names an explicit alternative or when-not-to-use condition, and doesn't contrast with alterlab_estimate_cost or alterlab_pricing, which are the nearest ambiguous siblings.

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