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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety and locality are covered. The description adds that the balance is USD-denominated and implicitly scoped to the authenticated account (no account argument exists), but says nothing about freshness, formatting, or whether the balance can be negative.

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?

One short sentence-fragment with no wasted words, and the key qualifier (USD) is front-loaded. It is arguably over-terse — a verb and a mention of the return shape would cost little and add clarity.

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 with no output schema, the description should say what comes back (a number, a string, a currency object) and whether values are live or cached. The annotation covers the safety profile, but the return-value gap leaves the definition only minimally sufficient.

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 zero parameters, which is the baseline-4 case; the schema is trivially complete. The description's "on this KeelRouter account" usefully confirms the account is implicit rather than a parameter, though it adds nothing further.

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 phrase "USD balance" names the exact resource and "on this KeelRouter account" scopes it, so an agent immediately knows this returns the account's USD balance. It is a noun fragment with no verb (the verb comes only from the title), and it draws no explicit contrast with siblings, which keeps it from a 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 guidance on when to call this versus alternatives, no prerequisites, and no exclusions. The agent must infer that this is the only balance-related tool among get_result, generate_image, generate_video, and list_models.

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