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

Annotations already establish the safe read-only/idempotent profile, so the bar is lower, and the description still adds real behavioral context: presets are not auto-applied, TDS on FD interest follows stored rules keyed to assessment_year, and the return shape is rows plus closing value and totals. It does not mention performance or limits, but for a pure calculator that is minor.

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?

Three sentences, front-loaded with what the tool computes and the no-plan scoping, then the caveat, then the return shape. The parenthetical parameter list is dense but each item earns its place by flagging which inputs drive the projection.

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 tool with nested SIP/rent objects and no output schema, the description covers the calculation model, the preset caveat, the tax rule dependency, and the return shape. Remaining gaps (defaults, interaction between maturity/sale months) are largely covered by the 100%-covered schema.

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 baseline is 3, but the description adds genuine semantics by naming the key inputs and warning that asset_class presets do not supply rates automatically — a behavior no per-field schema description conveys. It does not clarify interactions such as maturity_month vs sale_month or income_mode vs income_frequency.

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 and resource ('Pure calculator for one asset'), enumerates the computed outputs (monthly value, invested, growth, income, TDS), and explicitly carves out scope with 'no plan needed', which separates it from simulate_plan. An agent can distinguish it from the loan_* siblings without opening any schema.

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 phrase 'no plan needed' implicitly routes plan-based work to simulate_plan, and 'class presets are NOT applied automatically, so pass explicit rates' is an actionable prerequisite that prevents a common misuse. It stops short of naming the sibling alternatives explicitly or stating when not to use this tool.

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