Retrieve the balance

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

Annotations already mark this as read-only, idempotent, and non-destructive. The description adds valuable behavior context beyond the annotations: the unit conversion (1,000,000 micro-USD = $1.00), the meaning of held_micros as reserved by live calls, and the required billing:read scope. It is fully consistent with the annotations.

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?

The description is compact and front-loaded: it immediately defines the resource and return fields, then adds the usage context and scope. Every sentence earns its place, with no redundant phrasing or repetition of the title.

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?

For a zero-parameter read-only tool with no output schema, the description provides all necessary information: return field names, units, the reserved-credit concept, the scope requirement, and when to call it. Nothing essential is missing for an agent to invoke or interpret the result.

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 has zero parameters and the schema description coverage is 100%, so there is nothing for the description to add about individual parameters. The description instead explains the meaning of the returned fields, which is the closest relevant semantic content. According to the baseline for 0 parameters, this is an appropriate score.

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 clearly identifies the tool as retrieving the account's prepaid credit and specifies the exact fields returned: balance_micros, held_micros, and available_micros. It is obviously distinct from most siblings, but it does not explicitly differentiate itself from related reporting tools like get_usage_summary or list_ledger_entries.

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?

The description says to check this before placing calls or starting campaigns, which gives a clear operational context for when the tool should be invoked. However, it does not name alternatives or provide exclusion criteria, so it stops short of a fully explicit when-to-use vs when-not-to-use guide.

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