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

Annotations already declare readOnlyHint=true, openWorldHint=true, and destructiveHint=false, so the safety profile is fully covered and the description needn't repeat it. The description does add behavior worth knowing — the balance is expressed in the customer's currency unless overridden — but says nothing about auth requirements, rate limits, or freshness of the computed balance.

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 stating what the balance comprises, followed by the endpoint for API-literate agents. No filler and no restatement of the title, which already says 'Get customer balance'.

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 must carry the return shape, and it does name the three balance components. It omits units/format details (sign convention for available credit, whether past due is a subset of outstanding), which keeps it from a 5, but for a two-parameter read tool it is essentially complete.

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 description coverage is 100%, so both parameters are already documented, and the baseline for that situation is 3. The description's `currency` reference and the 'default: the customer's currency' phrasing reinforce the schema's documented default but add no new syntax or constraint detail.

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 states a specific resource (customer balance) and enumerates exactly what the value contains: total outstanding, past due, and available credit. That distinguishes it from siblings like invoiced_get_customer, which returns the customer record rather than a financial summary. It stops short of naming the sibling it differs from, so it lands at 4 rather than 5.

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 and no alternatives named, even though invoiced_get_customer and invoiced_list_invoices are plausible neighbors an agent might confuse it with. The only routing signal is the raw endpoint path, which assumes the agent knows the Invoiced API surface.

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