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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the description spends its space on what the annotations cannot say: the three budget-derivation routes (total_budget, income x percent, saved + savings x months), the split fallbacks, and the returned fields including card interest. It stops short of describing precision/rounding, currency assumptions beyond USD examples, or the exact default 3/6/12-month interest table output.

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?

Front-loaded with the usage trigger and examples, then budget routes, then outputs, then the sibling disclaimer — a sensible order. It is dense and long-ish, with the four quoted example phrases bordering on redundant given the schema's own examples, but every sentence still carries routing or output information.

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 12-parameter tool with no output schema, the description covers the trigger conditions, all three budget sources, all three split modes, the optional card-interest branch, the returned values, and the sibling boundary. Nothing an agent needs to call 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%, so baseline is 3, but the description adds genuinely new semantics: the precedence among the mutually exclusive budget routes and the split-mode inference (percent if percents present, amount if amounts, else equal). It does not explain interactions like what happens if total_budget and monthly_income are both supplied.

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 computation (splitting a holiday gift budget across people, optionally costing card interest) and anchors it to recognizable user phrasings. It explicitly carves out scope from the sibling calculate_holiday_budget, which handles travel/food/decor.

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?

Opens with an explicit 'Use when...' trigger plus four realistic utterance examples, and names the alternative tool and the condition that selects it. An agent can route between this and calculate_holiday_budget without opening either schema.

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