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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered without the description. The description adds that this is a deterministic savings computation and names currency-denominated outputs (EUR fields, early_repayment_eur), which is modestly useful context beyond the annotations.

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?

Two sentences, front-loaded with the purpose before the return fields, and no filler. The returns block is somewhat redundant given an output schema exists, which keeps it just short of a 5.

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 deterministic calculator with full annotations, 100% schema coverage, and an output schema, the description is nearly sufficient. It leaves one real gap: it does not explain the implied interest rate derivation, which an agent needs to understand to pass sensible inputs.

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 every parameter carries its own description and the baseline is 3. The description adds no format, unit-of-measure, or relationship guidance beyond what the schema states — notably it never explains how the interest rate is derived from remaining_capital, monthly_payment, and months_remaining.

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?

States a specific verb (Calculate), a precise resource (interest savings from early partial loan repayment), and the exact output semantics. It is clearly distinguishable from adjacent siblings such as calculate_loan_payment, calculate_mortgage, and calculate_housing_loan_comparison.

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?

The only routing hint is 'See list_bundles for related finance-universal calculators,' which points at a catalogue rather than stating when this tool is the right choice. There is no mention of when to prefer it over calculate_loan_payment or other amortization tools, and no stated prerequisites or exclusions.

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