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

Annotations already declare readOnlyHint, idempotentHint and non-destructive, so the safety profile is covered. The description adds that it returns months to goal, but with an output schema present that is not a large contribution, and it discloses nothing about edge cases (e.g. zero/negative rate, unreachable targets).

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?

Roughly three short sentences, front-loaded with the purpose before the input list and the bundle pointer. No filler, though the trailing list_bundles sentence is only marginally useful to an agent already selecting this tool.

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?

Because an output schema exists, the description does not need to explain return values, and the annotations cover safety. However, the mismatch between the advertised inputs (including 'current savings') and the actual required parameters leaves the agent unsure what this calculator actually solves for, which is a meaningful gap for a financial computation tool.

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 the baseline would be 3, but the description introduces a phantom input: it lists 'current savings' and 'monthly contribution' as inputs, while the schema has only target_amount, monthly_savings and annual_rate — there is no current savings parameter. It also says it computes 'monthly contribution needed' while monthly_savings is a required input, which muddies whether that value is solved for or 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 concrete verb and resource ('Compute time ... to reach a savings target') and anchors it in goal-based personal finance, which is enough to tell it apart from the many other finance calculators in the sibling list. It stops short of naming a specific alternative calculator, so it is clear but not differentiating.

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?

'Use for goal-based personal finance' gives an implied domain but no when/when-not condition and no real alternative routing. The pointer to list_bundles for 'finance-universal' calculators is a discovery hint rather than a selection rule between this tool and e.g. calculate_retirement_savings_gap or calculate_compound_interest.

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