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

Annotations already declare readOnlyHint=true, so safety is covered; the description's added value is explaining what the three balance components mean, notably that 'held' credits are tied to running generations. It does not discuss refresh/staleness or whether the balance is per-user or per-workspace. The idempotentHint=false annotation is slightly odd for a zero-argument read, but the description does not contradict it.

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?

A single front-loaded sentence with zero filler; the three balance categories and the credit-to-USD rate are the only facts an agent needs to interpret the numbers.

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 an output schema present, return formatting is already documented, and the description supplies the units and semantics ('1 credit = 0.01 USD') needed to read those values correctly. The only gap is a note on whether held credits fluctuate as generations run, which would matter for repeated calls.

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 the baseline applies. There is nothing for the description to disambiguate, and it does not waste words on nonexistent inputs.

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?

The description identifies the exact resource ('the user's Arumi credits') and enumerates the three sub-balances it reports: available, held by running generations, and owed. It is clearly distinguishable from siblings like get_generation or quote. It stops short of an explicit verb ('retrieve/return'), but the resource is specific enough that an agent knows what it gets.

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 guidance, no prerequisites, and no mention of alternatives. An agent must infer on its own that this is the tool to call before generate to check whether credits suffice, and nothing warns about when the balance is stale or changes.

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