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

With no annotations, the description carries the burden and delivers substantive behavior: fixed-then-variable phases, monthly and lump-sum overpayments, interest-only mechanics ('minimum payments track the remaining balance, with principal due at maturity'), and unsupported KFIK/cash-collateral modes. It also imposes input-integrity rules ('never substitute example loan terms or rates', EUR amounts and APR expected). Not fully disclosed are determinism/statelessness and rounding conventions on the produced schedule.

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 front-loaded paragraph that leads with the purpose, then capabilities, then exclusions, then input requirements — good ordering. Slight bloat in the trailing meta-instruction ('without narrating tool selection'), which is agent-directed rather than tool-descriptive.

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 16-parameter, annotation-free calculator, the description supplies the capability scope, the exclusion set, the input-integrity contract, and the currency/rate conventions, while the output schema covers return values and the schema covers each parameter's type and bounds. Nothing an agent needs to invoke 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 the schema already documents every parameter including enums and ranges; baseline is 3. The description adds useful framing — which inputs are mandatory in practice (actual loan amount, term, fixed-period length, rate inputs per applicable phase), the EUR/APR units, and the prohibition on fabricated example values — but it does not explain parameter interactions such as bankMargin vs variableBaseRate or overpaymentPeriodType/overpaymentYearsCount beyond what the schema states.

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?

Opens with a specific verb and resource: 'Simulates a Cyprus mortgage with a payment schedule that reconciles paid amounts to principal and interest.' The Cyprus/mortgage framing plus the amortization-and-reconciliation scope clearly separates it from siblings like audit_mortgage_statement, parse_mortgage_statement_text and compare_rent_vs_buy.

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?

Gives explicit when-to-use ('estimate a Cyprus mortgage payment, amortization, overpayments or rate scenarios') and when-not ('For document checklists or general mortgage information, do not call the calculator; answer or research directly'), plus an unsupported-configuration exclusion (KFIK and cash-collateral). An agent can route correctly without inference.

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