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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description's job is to add computation semantics — and it does, disclosing that compounding is monthly and that the deposit stream is optional. It also names the returned figures, which matters since no output schema exists. It does not say whether deposits land at the start or end of each month, which is the main remaining ambiguity.

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 sentence with zero filler: the core mechanic (monthly compounding, optional deposit) comes first and the return values are packed into the same line. Nothing is repeated from annotations or schema.

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 four-parameter pure-computation tool with no output schema, the description supplies both the compounding convention and the three expected return values, which is most of what an agent needs. Only timing of deposits and rounding/currency conventions are left unstated.

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 all four parameters (including bounds like the 60-year cap and 100% rate cap) are already documented. The description only adds that the deposit is 'optional' and recurring monthly, which the schema states as 'Added each month. Default 0.' Baseline 3 applies.

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 the specific computation (savings growth with monthly compounding and an optional monthly deposit) and enumerates the three outputs, which distinguishes it from the loan/mortgage/ROI siblings. It lacks an explicit verb phrase like 'Calculate', but the resource and result set are unambiguous.

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?

Usage is implied by the 'savings growth' framing, but the description never says when to prefer this over loan_repayment_calculator, mortgage_calculator, or roi_calculator, nor does it state any prerequisites or exclusions. An agent must infer routing from the name alone.

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